diff --git a/changes/bug34078 b/changes/bug34078
new file mode 100644
index 0000000000..1015d24547
--- /dev/null
+++ b/changes/bug34078
@@ -0,0 +1,5 @@
+  o Minor bugfixes (compiler compatibility):
+    - Avoid compiler warnings from Clang 10 related to the use of
+      GCC-style "/* falls through */" comments.  Both Clang and GCC allow
+      __attribute__((fallthrough)) instead, so that's what we're using now.
+      Fixes bug 34078; bugfix on 0.3.1.3-alpha.
diff --git a/src/app/config/quiet_level.c b/src/app/config/quiet_level.c
index 4e17978228..e04faaef3a 100644
--- a/src/app/config/quiet_level.c
+++ b/src/app/config/quiet_level.c
@@ -31,7 +31,7 @@ add_default_log_for_quiet_level(quiet_level_t quiet)
     /* --hush: log at warning or higher. */
       add_default_log(LOG_WARN);
       break;
-    case QUIET_NONE: /* fall through */
+    case QUIET_NONE: FALLTHROUGH;
     default:
       add_default_log(LOG_NOTICE);
   }
diff --git a/src/core/or/channeltls.c b/src/core/or/channeltls.c
index 8112eb64e2..efa8e2d891 100644
--- a/src/core/or/channeltls.c
+++ b/src/core/or/channeltls.c
@@ -1238,7 +1238,7 @@ channel_tls_handle_var_cell(var_cell_t *var_cell, or_connection_t *conn)
       /* But that should be happening any longer've disabled bufferevents. */
       tor_assert_nonfatal_unreached_once();
 
-      /* fall through */
+      FALLTHROUGH;
     case OR_CONN_STATE_TLS_SERVER_RENEGOTIATING:
       if (!(command_allowed_before_handshake(var_cell->command))) {
         log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
diff --git a/src/core/or/circuitbuild.c b/src/core/or/circuitbuild.c
index 03ed2c7d29..4865d05d98 100644
--- a/src/core/or/circuitbuild.c
+++ b/src/core/or/circuitbuild.c
@@ -2108,7 +2108,7 @@ choose_good_exit_server(origin_circuit_t *circ,
       /* For these three, we want to pick the exit like a middle hop,
        * since it should be random. */
       tor_assert_nonfatal(is_internal);
-      /* Falls through */
+      FALLTHROUGH;
     case CIRCUIT_PURPOSE_C_GENERAL:
       if (is_internal) /* pick it like a middle hop */
         return router_choose_random_node(NULL, options->ExcludeNodes, flags);
diff --git a/src/core/or/circuitlist.c b/src/core/or/circuitlist.c
index 6a712926a3..2120c1e85d 100644
--- a/src/core/or/circuitlist.c
+++ b/src/core/or/circuitlist.c
@@ -846,7 +846,7 @@ circuit_purpose_to_controller_hs_state_string(uint8_t purpose)
              "Unrecognized circuit purpose: %d",
              (int)purpose);
       tor_fragile_assert();
-      /* fall through */
+      FALLTHROUGH;
 
     case CIRCUIT_PURPOSE_OR:
     case CIRCUIT_PURPOSE_C_GENERAL:
diff --git a/src/core/or/circuituse.c b/src/core/or/circuituse.c
index 5d10cacc71..37af449106 100644
--- a/src/core/or/circuituse.c
+++ b/src/core/or/circuituse.c
@@ -780,7 +780,7 @@ circuit_expire_building(void)
         if (!hs_circ_is_rend_sent_in_intro1(CONST_TO_ORIGIN_CIRCUIT(victim))) {
           break;
         }
-        /* fallthrough! */
+        FALLTHROUGH;
       case CIRCUIT_PURPOSE_C_INTRODUCE_ACK_WAIT:
       case CIRCUIT_PURPOSE_C_REND_READY_INTRO_ACKED:
         /* If we have reached this line, we want to spare the circ for now. */
diff --git a/src/core/or/connection_edge.c b/src/core/or/connection_edge.c
index aeb9ec6460..7f707a5660 100644
--- a/src/core/or/connection_edge.c
+++ b/src/core/or/connection_edge.c
@@ -307,7 +307,7 @@ connection_edge_process_inbuf(edge_connection_t *conn, int package_partial)
         note_user_activity(approx_time());
       }
 
-      /* falls through. */
+      FALLTHROUGH;
     case EXIT_CONN_STATE_OPEN:
       if (connection_edge_package_raw_inbuf(conn, package_partial, NULL) < 0) {
         /* (We already sent an end cell if possible) */
@@ -332,7 +332,7 @@ connection_edge_process_inbuf(edge_connection_t *conn, int package_partial)
       }
       /* Fall through if the connection is on a circuit without optimistic
        * data support. */
-      /* Falls through. */
+      FALLTHROUGH;
     case EXIT_CONN_STATE_CONNECTING:
     case AP_CONN_STATE_RENDDESC_WAIT:
     case AP_CONN_STATE_CIRCUIT_WAIT:
@@ -766,7 +766,7 @@ connection_edge_flushed_some(edge_connection_t *conn)
         note_user_activity(approx_time());
       }
 
-      /* falls through. */
+      FALLTHROUGH;
     case EXIT_CONN_STATE_OPEN:
       sendme_connection_edge_consider_sending(conn);
       break;
diff --git a/src/core/or/crypt_path.c b/src/core/or/crypt_path.c
index 9296b00208..8f41540848 100644
--- a/src/core/or/crypt_path.c
+++ b/src/core/or/crypt_path.c
@@ -113,7 +113,7 @@ cpath_assert_layer_ok(const crypt_path_t *cp)
     {
     case CPATH_STATE_OPEN:
       relay_crypto_assert_ok(&cp->pvt_crypto);
-      /* fall through */
+      FALLTHROUGH;
     case CPATH_STATE_CLOSED:
       /*XXXX Assert that there's no handshake_state either. */
       tor_assert(!cp->rend_dh_handshake_state);
diff --git a/src/core/or/onion.c b/src/core/or/onion.c
index 4a5b296b9e..21bda79914 100644
--- a/src/core/or/onion.c
+++ b/src/core/or/onion.c
@@ -509,7 +509,7 @@ create_cell_format_impl(cell_t *cell_out, const create_cell_t *cell_in,
       p += 16;
       space -= 16;
     }
-    /* Fall through */
+    FALLTHROUGH;
   case CELL_CREATE_FAST:
     tor_assert(cell_in->handshake_len <= space);
     memcpy(p, cell_in->onionskin, cell_in->handshake_len);
diff --git a/src/core/or/policies.c b/src/core/or/policies.c
index a82995fe12..4a69854deb 100644
--- a/src/core/or/policies.c
+++ b/src/core/or/policies.c
@@ -2788,7 +2788,7 @@ parse_short_policy(const char *summary)
     switch (*next) {
       case ',':
         ++next;
-        /* fall through */
+        FALLTHROUGH;
       case '\0':
         high = low;
         break;
diff --git a/src/core/or/reasons.c b/src/core/or/reasons.c
index b60dfdf275..7da7843cab 100644
--- a/src/core/or/reasons.c
+++ b/src/core/or/reasons.c
@@ -489,7 +489,7 @@ end_reason_to_http_connect_response_line(int endreason)
       return "HTTP/1.0 502 Bad Gateway (tor protocol violation)\r\n\r\n";
     case END_STREAM_REASON_ENTRYPOLICY:
       return "HTTP/1.0 403 Forbidden (entry policy violation)\r\n\r\n";
-    case END_STREAM_REASON_NOTDIRECTORY: /* Fall Through */
+    case END_STREAM_REASON_NOTDIRECTORY: FALLTHROUGH;
     default:
       tor_assert_nonfatal_unreached();
       return "HTTP/1.0 500 Internal Server Error (weird end reason)\r\n\r\n";
diff --git a/src/core/or/relay.c b/src/core/or/relay.c
index 5ddabf3474..82353e311f 100644
--- a/src/core/or/relay.c
+++ b/src/core/or/relay.c
@@ -940,7 +940,7 @@ connection_ap_process_end_not_open(
           break; /* break means it'll close, below */
         /* Else fall through: expire this circuit, clear the
          * chosen_exit_name field, and try again. */
-        /* Falls through. */
+        FALLTHROUGH;
       case END_STREAM_REASON_RESOLVEFAILED:
       case END_STREAM_REASON_TIMEOUT:
       case END_STREAM_REASON_MISC:
diff --git a/src/core/or/scheduler.c b/src/core/or/scheduler.c
index cd9aa54642..a3869c7ae3 100644
--- a/src/core/or/scheduler.c
+++ b/src/core/or/scheduler.c
@@ -191,7 +191,7 @@ get_scheduler_type_string(scheduler_types_t type)
   case SCHEDULER_KIST_LITE:
     return "KISTLite";
   case SCHEDULER_NONE:
-    /* fallthrough */
+    FALLTHROUGH;
   default:
     tor_assert_unreached();
     return "(N/A)";
@@ -287,7 +287,7 @@ select_scheduler(void)
       scheduler_kist_set_lite_mode();
       goto end;
     case SCHEDULER_NONE:
-      /* fallthrough */
+      FALLTHROUGH;
     default:
       /* Our option validation should have caught this. */
       tor_assert_unreached();
diff --git a/src/core/or/sendme.c b/src/core/or/sendme.c
index db3e2e94fd..788f56088c 100644
--- a/src/core/or/sendme.c
+++ b/src/core/or/sendme.c
@@ -293,7 +293,7 @@ send_circuit_level_sendme(circuit_t *circ, crypt_path_t *layer_hint,
     log_debug(LD_PROTOCOL, "Emitting SENDME version 1 cell.");
     break;
   case 0x00:
-    /* Fallthrough because default is to use v0. */
+    FALLTHROUGH;
   default:
     /* Unknown version, fallback to version 0 meaning no payload. */
     payload_len = 0;
diff --git a/src/core/proto/proto_socks.c b/src/core/proto/proto_socks.c
index 697fc683c5..4f39d69d62 100644
--- a/src/core/proto/proto_socks.c
+++ b/src/core/proto/proto_socks.c
@@ -861,7 +861,7 @@ fetch_from_buf_socks(buf_t *buf, socks_request_t *req,
       case SOCKS_RESULT_TRUNCATED:
         if (datalen == n_pullup)
           return 0;
-        /* FALLTHRU */
+        FALLTHROUGH;
       case SOCKS_RESULT_MORE_EXPECTED:
         res = 0;
         break;
@@ -967,7 +967,7 @@ parse_socks(const char *data, size_t datalen, socks_request_t *req,
       strlcpy((char*)req->reply, SOCKS_PROXY_IS_NOT_AN_HTTP_PROXY_MSG,
               MAX_SOCKS_REPLY_LEN);
       req->replylen = strlen((char*)req->reply)+1;
-      /* fall through */
+      FALLTHROUGH;
     default: /* version is not socks4 or socks5 */
       log_warn(LD_APP,
                "Socks version %d not recognized. (This port is not an "
diff --git a/src/ext/csiphash.c b/src/ext/csiphash.c
index faa52ae4e1..e0f5b2e5c9 100644
--- a/src/ext/csiphash.c
+++ b/src/ext/csiphash.c
@@ -95,13 +95,13 @@ uint64_t siphash24(const void *src, unsigned long src_sz, const struct sipkey *k
 	}
 #else
 	switch (src_sz - blocks) {
-		case 7: last7 |= (uint64_t)m[i + 6] << 48; /* Falls through. */
-		case 6: last7 |= (uint64_t)m[i + 5] << 40; /* Falls through. */
-		case 5:	last7 |= (uint64_t)m[i + 4] << 32; /* Falls through. */
-		case 4: last7 |= (uint64_t)m[i + 3] << 24; /* Falls through. */
-		case 3:	last7 |= (uint64_t)m[i + 2] << 16; /* Falls through. */
-		case 2:	last7 |= (uint64_t)m[i + 1] <<  8; /* Falls through. */
-		case 1: last7 |= (uint64_t)m[i + 0]      ; /* Falls through. */
+		case 7: last7 |= (uint64_t)m[i + 6] << 48; FALLTHROUGH;
+		case 6: last7 |= (uint64_t)m[i + 5] << 40; FALLTHROUGH;
+		case 5:	last7 |= (uint64_t)m[i + 4] << 32; FALLTHROUGH;
+		case 4: last7 |= (uint64_t)m[i + 3] << 24; FALLTHROUGH;
+		case 3:	last7 |= (uint64_t)m[i + 2] << 16; FALLTHROUGH;
+		case 2:	last7 |= (uint64_t)m[i + 1] <<  8; FALLTHROUGH;
+		case 1: last7 |= (uint64_t)m[i + 0]      ; FALLTHROUGH;
 		case 0:
 		default:;
 	}
diff --git a/src/ext/ed25519/donna/modm-donna-32bit.h b/src/ext/ed25519/donna/modm-donna-32bit.h
index 0ef9e58fa1..5934d9ca9d 100644
--- a/src/ext/ed25519/donna/modm-donna-32bit.h
+++ b/src/ext/ed25519/donna/modm-donna-32bit.h
@@ -385,14 +385,14 @@ sub256_modm_batch(bignum256modm out, const bignum256modm a, const bignum256modm
 	size_t i = 0;
 	bignum256modm_element_t carry = 0;
 	switch (limbsize) {
-		case 8: out[i] = (a[i] - b[i]) - carry; carry = (out[i] >> 31); out[i] &= 0x3fffffff; i++; /* Falls through. */
-		case 7: out[i] = (a[i] - b[i]) - carry; carry = (out[i] >> 31); out[i] &= 0x3fffffff; i++; /* Falls through. */
-		case 6: out[i] = (a[i] - b[i]) - carry; carry = (out[i] >> 31); out[i] &= 0x3fffffff; i++; /* Falls through. */
-		case 5: out[i] = (a[i] - b[i]) - carry; carry = (out[i] >> 31); out[i] &= 0x3fffffff; i++; /* Falls through. */
-		case 4: out[i] = (a[i] - b[i]) - carry; carry = (out[i] >> 31); out[i] &= 0x3fffffff; i++; /* Falls through. */
-		case 3: out[i] = (a[i] - b[i]) - carry; carry = (out[i] >> 31); out[i] &= 0x3fffffff; i++; /* Falls through. */
-		case 2: out[i] = (a[i] - b[i]) - carry; carry = (out[i] >> 31); out[i] &= 0x3fffffff; i++; /* Falls through. */
-		case 1: out[i] = (a[i] - b[i]) - carry; carry = (out[i] >> 31); out[i] &= 0x3fffffff; i++; /* Falls through. */
+		case 8: out[i] = (a[i] - b[i]) - carry; carry = (out[i] >> 31); out[i] &= 0x3fffffff; i++; FALLTHROUGH;
+		case 7: out[i] = (a[i] - b[i]) - carry; carry = (out[i] >> 31); out[i] &= 0x3fffffff; i++; FALLTHROUGH;
+		case 6: out[i] = (a[i] - b[i]) - carry; carry = (out[i] >> 31); out[i] &= 0x3fffffff; i++; FALLTHROUGH;
+		case 5: out[i] = (a[i] - b[i]) - carry; carry = (out[i] >> 31); out[i] &= 0x3fffffff; i++; FALLTHROUGH;
+		case 4: out[i] = (a[i] - b[i]) - carry; carry = (out[i] >> 31); out[i] &= 0x3fffffff; i++; FALLTHROUGH;
+		case 3: out[i] = (a[i] - b[i]) - carry; carry = (out[i] >> 31); out[i] &= 0x3fffffff; i++; FALLTHROUGH;
+		case 2: out[i] = (a[i] - b[i]) - carry; carry = (out[i] >> 31); out[i] &= 0x3fffffff; i++; FALLTHROUGH;
+		case 1: out[i] = (a[i] - b[i]) - carry; carry = (out[i] >> 31); out[i] &= 0x3fffffff; i++; FALLTHROUGH;
 		case 0: 
 		default: out[i] = (a[i] - b[i]) - carry;
 	}
@@ -403,14 +403,14 @@ sub256_modm_batch(bignum256modm out, const bignum256modm a, const bignum256modm
 static int
 lt256_modm_batch(const bignum256modm a, const bignum256modm b, size_t limbsize) {
 	switch (limbsize) {
-		case 8: if (a[8] > b[8]) return 0; if (a[8] < b[8]) return 1; /* Falls through. */
-		case 7: if (a[7] > b[7]) return 0; if (a[7] < b[7]) return 1; /* Falls through. */
-		case 6: if (a[6] > b[6]) return 0; if (a[6] < b[6]) return 1; /* Falls through. */
-		case 5: if (a[5] > b[5]) return 0; if (a[5] < b[5]) return 1; /* Falls through. */
-		case 4: if (a[4] > b[4]) return 0; if (a[4] < b[4]) return 1; /* Falls through. */
-		case 3: if (a[3] > b[3]) return 0; if (a[3] < b[3]) return 1; /* Falls through. */
-		case 2: if (a[2] > b[2]) return 0; if (a[2] < b[2]) return 1; /* Falls through. */
-		case 1: if (a[1] > b[1]) return 0; if (a[1] < b[1]) return 1; /* Falls through. */
+		case 8: if (a[8] > b[8]) return 0; if (a[8] < b[8]) return 1; FALLTHROUGH;
+		case 7: if (a[7] > b[7]) return 0; if (a[7] < b[7]) return 1; FALLTHROUGH;
+		case 6: if (a[6] > b[6]) return 0; if (a[6] < b[6]) return 1; FALLTHROUGH;
+		case 5: if (a[5] > b[5]) return 0; if (a[5] < b[5]) return 1; FALLTHROUGH;
+		case 4: if (a[4] > b[4]) return 0; if (a[4] < b[4]) return 1; FALLTHROUGH;
+		case 3: if (a[3] > b[3]) return 0; if (a[3] < b[3]) return 1; FALLTHROUGH;
+		case 2: if (a[2] > b[2]) return 0; if (a[2] < b[2]) return 1; FALLTHROUGH;
+		case 1: if (a[1] > b[1]) return 0; if (a[1] < b[1]) return 1; FALLTHROUGH;
 		case 0: if (a[0] > b[0]) return 0; if (a[0] < b[0]) return 1;
 	}
 	return 0;
@@ -420,14 +420,14 @@ lt256_modm_batch(const bignum256modm a, const bignum256modm b, size_t limbsize)
 static int
 lte256_modm_batch(const bignum256modm a, const bignum256modm b, size_t limbsize) {
 	switch (limbsize) {
-		case 8: if (a[8] > b[8]) return 0; if (a[8] < b[8]) return 1; /* Falls through. */
-		case 7: if (a[7] > b[7]) return 0; if (a[7] < b[7]) return 1; /* Falls through. */
-		case 6: if (a[6] > b[6]) return 0; if (a[6] < b[6]) return 1; /* Falls through. */
-		case 5: if (a[5] > b[5]) return 0; if (a[5] < b[5]) return 1; /* Falls through. */
-		case 4: if (a[4] > b[4]) return 0; if (a[4] < b[4]) return 1; /* Falls through. */
-		case 3: if (a[3] > b[3]) return 0; if (a[3] < b[3]) return 1; /* Falls through. */
-		case 2: if (a[2] > b[2]) return 0; if (a[2] < b[2]) return 1; /* Falls through. */
-		case 1: if (a[1] > b[1]) return 0; if (a[1] < b[1]) return 1; /* Falls through. */
+		case 8: if (a[8] > b[8]) return 0; if (a[8] < b[8]) return 1; FALLTHROUGH;
+		case 7: if (a[7] > b[7]) return 0; if (a[7] < b[7]) return 1; FALLTHROUGH;
+		case 6: if (a[6] > b[6]) return 0; if (a[6] < b[6]) return 1; FALLTHROUGH;
+		case 5: if (a[5] > b[5]) return 0; if (a[5] < b[5]) return 1; FALLTHROUGH;
+		case 4: if (a[4] > b[4]) return 0; if (a[4] < b[4]) return 1; FALLTHROUGH;
+		case 3: if (a[3] > b[3]) return 0; if (a[3] < b[3]) return 1; FALLTHROUGH;
+		case 2: if (a[2] > b[2]) return 0; if (a[2] < b[2]) return 1; FALLTHROUGH;
+		case 1: if (a[1] > b[1]) return 0; if (a[1] < b[1]) return 1; FALLTHROUGH;
 		case 0: if (a[0] > b[0]) return 0; if (a[0] < b[0]) return 1;
 	}
 	return 1;
diff --git a/src/ext/ed25519/donna/modm-donna-64bit.h b/src/ext/ed25519/donna/modm-donna-64bit.h
index 06c98e3039..aa361afdbc 100644
--- a/src/ext/ed25519/donna/modm-donna-64bit.h
+++ b/src/ext/ed25519/donna/modm-donna-64bit.h
@@ -294,10 +294,10 @@ sub256_modm_batch(bignum256modm out, const bignum256modm a, const bignum256modm
 	size_t i = 0;
 	bignum256modm_element_t carry = 0;
 	switch (limbsize) {
-		case 4: out[i] = (a[i] - b[i])        ; carry = (out[i] >> 63); out[i] &= 0xffffffffffffff; i++; /* Falls through. */
-		case 3: out[i] = (a[i] - b[i]) - carry; carry = (out[i] >> 63); out[i] &= 0xffffffffffffff; i++; /* Falls through. */
-		case 2:	out[i] = (a[i] - b[i]) - carry; carry = (out[i] >> 63); out[i] &= 0xffffffffffffff; i++; /* Falls through. */
-		case 1:	out[i] = (a[i] - b[i]) - carry; carry = (out[i] >> 63); out[i] &= 0xffffffffffffff; i++; /* Falls through. */
+		case 4: out[i] = (a[i] - b[i])        ; carry = (out[i] >> 63); out[i] &= 0xffffffffffffff; i++; FALLTHROUGH;
+		case 3: out[i] = (a[i] - b[i]) - carry; carry = (out[i] >> 63); out[i] &= 0xffffffffffffff; i++; FALLTHROUGH;
+		case 2:	out[i] = (a[i] - b[i]) - carry; carry = (out[i] >> 63); out[i] &= 0xffffffffffffff; i++; FALLTHROUGH;
+		case 1:	out[i] = (a[i] - b[i]) - carry; carry = (out[i] >> 63); out[i] &= 0xffffffffffffff; i++; FALLTHROUGH;
 		case 0: 
 		default: out[i] = (a[i] - b[i]) - carry;
 	}
@@ -310,10 +310,10 @@ lt256_modm_batch(const bignum256modm a, const bignum256modm b, size_t limbsize)
 	size_t i = 0;
 	bignum256modm_element_t t, carry = 0;
 	switch (limbsize) {
-		case 4: t = (a[i] - b[i])        ; carry = (t >> 63); i++; /* Falls through. */
-		case 3: t = (a[i] - b[i]) - carry; carry = (t >> 63); i++; /* Falls through. */
-		case 2: t = (a[i] - b[i]) - carry; carry = (t >> 63); i++; /* Falls through. */
-		case 1: t = (a[i] - b[i]) - carry; carry = (t >> 63); i++; /* Falls through. */
+		case 4: t = (a[i] - b[i])        ; carry = (t >> 63); i++; FALLTHROUGH;
+		case 3: t = (a[i] - b[i]) - carry; carry = (t >> 63); i++; FALLTHROUGH;
+		case 2: t = (a[i] - b[i]) - carry; carry = (t >> 63); i++; FALLTHROUGH;
+		case 1: t = (a[i] - b[i]) - carry; carry = (t >> 63); i++; FALLTHROUGH;
 		case 0: t = (a[i] - b[i]) - carry; carry = (t >> 63);
 	}
 	return (int)carry;
@@ -325,10 +325,10 @@ lte256_modm_batch(const bignum256modm a, const bignum256modm b, size_t limbsize)
 	size_t i = 0;
 	bignum256modm_element_t t, carry = 0;
 	switch (limbsize) {
-		case 4: t = (b[i] - a[i])        ; carry = (t >> 63); i++; /* Falls through. */
-		case 3: t = (b[i] - a[i]) - carry; carry = (t >> 63); i++; /* Falls through. */
-		case 2: t = (b[i] - a[i]) - carry; carry = (t >> 63); i++; /* Falls through. */
-		case 1: t = (b[i] - a[i]) - carry; carry = (t >> 63); i++; /* Falls through. */
+		case 4: t = (b[i] - a[i])        ; carry = (t >> 63); i++; FALLTHROUGH;
+		case 3: t = (b[i] - a[i]) - carry; carry = (t >> 63); i++; FALLTHROUGH;
+		case 2: t = (b[i] - a[i]) - carry; carry = (t >> 63); i++; FALLTHROUGH;
+		case 1: t = (b[i] - a[i]) - carry; carry = (t >> 63); i++; FALLTHROUGH;
 		case 0: t = (b[i] - a[i]) - carry; carry = (t >> 63);
 	}
 	return (int)!carry;
diff --git a/src/feature/client/entrynodes.c b/src/feature/client/entrynodes.c
index 8962f65006..749d8881f0 100644
--- a/src/feature/client/entrynodes.c
+++ b/src/feature/client/entrynodes.c
@@ -2263,7 +2263,7 @@ entry_guards_note_guard_success(guard_selection_t *gs,
       break;
     default:
       tor_assert_nonfatal_unreached();
-      /* Fall through. */
+      FALLTHROUGH;
     case GUARD_CIRC_STATE_USABLE_IF_NO_BETTER_GUARD:
       if (guard->is_primary) {
         /* XXXX #20832 -- I don't actually like this logic. It seems to make
diff --git a/src/feature/control/control_cmd.c b/src/feature/control/control_cmd.c
index c2d23243e5..8259c3b353 100644
--- a/src/feature/control/control_cmd.c
+++ b/src/feature/control/control_cmd.c
@@ -1904,7 +1904,7 @@ handle_control_add_onion(control_connection_t *conn,
   case RSAE_BADAUTH:
     control_write_endreply(conn, 512, "Invalid client authorization");
     break;
-  case RSAE_INTERNAL: /* FALLSTHROUGH */
+  case RSAE_INTERNAL: FALLTHROUGH;
   default:
     control_write_endreply(conn, 551, "Failed to add Onion Service");
   }
diff --git a/src/feature/dirclient/dirclient.c b/src/feature/dirclient/dirclient.c
index 1b6eed12f0..1200c3c562 100644
--- a/src/feature/dirclient/dirclient.c
+++ b/src/feature/dirclient/dirclient.c
@@ -1365,7 +1365,7 @@ directory_initiate_request,(directory_request_t *request))
       case 1:
         /* start flushing conn */
         conn->base_.state = DIR_CONN_STATE_CLIENT_SENDING;
-        /* fall through */
+        FALLTHROUGH;
       case 0:
         /* queue the command on the outbuf */
         directory_send_command(conn, 1, request);
diff --git a/src/feature/dirparse/parsecommon.c b/src/feature/dirparse/parsecommon.c
index 0c63cd4846..ab465c4d7f 100644
--- a/src/feature/dirparse/parsecommon.c
+++ b/src/feature/dirparse/parsecommon.c
@@ -222,7 +222,7 @@ token_check_object(memarea_t *area, const char *kwd,
                      kwd, crypto_pk_num_bits(tok->key));
         RET_ERR(ebuf);
       }
-      /* fall through */
+      FALLTHROUGH;
     case NEED_KEY: /* There must be some kind of key. */
       if (!tok->key) {
         tor_snprintf(ebuf, sizeof(ebuf), "Missing public key for %s", kwd);
diff --git a/src/feature/relay/dns.c b/src/feature/relay/dns.c
index 9639193685..7ab4ca0f45 100644
--- a/src/feature/relay/dns.c
+++ b/src/feature/relay/dns.c
@@ -548,7 +548,7 @@ send_resolved_cell,(edge_connection_t *conn, uint8_t answer_type,
         answer_type = RESOLVED_TYPE_ERROR;
         /* We let this fall through and treat it as an error. */
       }
-      /* Falls through. */
+      FALLTHROUGH;
     case RESOLVED_TYPE_ERROR_TRANSIENT:
     case RESOLVED_TYPE_ERROR:
       {
diff --git a/src/feature/rend/rendclient.c b/src/feature/rend/rendclient.c
index cc55065fdd..09db7045fa 100644
--- a/src/feature/rend/rendclient.c
+++ b/src/feature/rend/rendclient.c
@@ -831,7 +831,7 @@ rend_client_report_intro_point_failure(extend_info_t *failed_intro,
         log_warn(LD_BUG, "Unknown failure type %u. Removing intro point.",
                  failure_type);
         tor_fragile_assert();
-        /* fall through */
+        FALLTHROUGH;
       case INTRO_POINT_FAILURE_GENERIC:
         rend_cache_intro_failure_note(failure_type,
                                       (uint8_t *)failed_intro->identity_digest,
diff --git a/src/lib/crypt_ops/crypto_digest_nss.c b/src/lib/crypt_ops/crypto_digest_nss.c
index 3092a08015..92c20fe9e8 100644
--- a/src/lib/crypt_ops/crypto_digest_nss.c
+++ b/src/lib/crypt_ops/crypto_digest_nss.c
@@ -37,8 +37,8 @@ digest_alg_to_nss_oid(digest_algorithm_t alg)
     case DIGEST_SHA1: return SEC_OID_SHA1;
     case DIGEST_SHA256: return SEC_OID_SHA256;
     case DIGEST_SHA512: return SEC_OID_SHA512;
-    case DIGEST_SHA3_256: /* Fall through */
-    case DIGEST_SHA3_512: /* Fall through */
+    case DIGEST_SHA3_256: FALLTHROUGH;
+    case DIGEST_SHA3_512: FALLTHROUGH;
     default:
       return SEC_OID_UNKNOWN;
   }
@@ -89,12 +89,12 @@ static bool
 library_supports_digest(digest_algorithm_t alg)
 {
   switch (alg) {
-    case DIGEST_SHA1: /* Fall through */
-    case DIGEST_SHA256: /* Fall through */
+    case DIGEST_SHA1: FALLTHROUGH;
+    case DIGEST_SHA256: FALLTHROUGH;
     case DIGEST_SHA512:
       return true;
-    case DIGEST_SHA3_256: /* Fall through */
-    case DIGEST_SHA3_512: /* Fall through */
+    case DIGEST_SHA3_256: FALLTHROUGH;
+    case DIGEST_SHA3_512: FALLTHROUGH;
     default:
       return false;
   }
@@ -201,8 +201,8 @@ crypto_digest_alloc_bytes(digest_algorithm_t alg)
 #define END_OF_FIELD(f) (offsetof(crypto_digest_t, f) + \
                          STRUCT_FIELD_SIZE(crypto_digest_t, f))
   switch (alg) {
-    case DIGEST_SHA1: /* Fall through */
-    case DIGEST_SHA256: /* Fall through */
+    case DIGEST_SHA1: FALLTHROUGH;
+    case DIGEST_SHA256: FALLTHROUGH;
     case DIGEST_SHA512:
       return END_OF_FIELD(d.ctx);
     case DIGEST_SHA3_256:
@@ -228,8 +228,8 @@ crypto_digest_new_internal(digest_algorithm_t algorithm)
 
   switch (algorithm)
     {
-    case DIGEST_SHA1: /* fall through */
-    case DIGEST_SHA256: /* fall through */
+    case DIGEST_SHA1: FALLTHROUGH;
+    case DIGEST_SHA256: FALLTHROUGH;
     case DIGEST_SHA512:
       r->d.ctx = PK11_CreateDigestContext(digest_alg_to_nss_oid(algorithm));
       if (BUG(!r->d.ctx)) {
@@ -316,8 +316,8 @@ crypto_digest_add_bytes(crypto_digest_t *digest, const char *data,
    * just doing it ourselves. Hashes are fast.
    */
   switch (digest->algorithm) {
-    case DIGEST_SHA1: /* fall through */
-    case DIGEST_SHA256: /* fall through */
+    case DIGEST_SHA1: FALLTHROUGH;
+    case DIGEST_SHA256: FALLTHROUGH;
     case DIGEST_SHA512:
       tor_assert(len <= UINT_MAX);
       SECStatus s = PK11_DigestOp(digest->d.ctx,
@@ -325,7 +325,7 @@ crypto_digest_add_bytes(crypto_digest_t *digest, const char *data,
                                   (unsigned int)len);
       tor_assert(s == SECSuccess);
       break;
-    case DIGEST_SHA3_256: /* FALLSTHROUGH */
+    case DIGEST_SHA3_256: FALLTHROUGH;
     case DIGEST_SHA3_512:
       keccak_digest_update(&digest->d.sha3, (const uint8_t *)data, len);
       break;
diff --git a/src/lib/crypt_ops/crypto_digest_openssl.c b/src/lib/crypt_ops/crypto_digest_openssl.c
index bc076df619..11189c7fb2 100644
--- a/src/lib/crypt_ops/crypto_digest_openssl.c
+++ b/src/lib/crypt_ops/crypto_digest_openssl.c
@@ -160,11 +160,11 @@ crypto_digest_alloc_bytes(digest_algorithm_t alg)
     case DIGEST_SHA512:
       return END_OF_FIELD(d.sha512);
 #ifdef OPENSSL_HAS_SHA3
-    case DIGEST_SHA3_256: /* Fall through */
+    case DIGEST_SHA3_256: FALLTHROUGH;
     case DIGEST_SHA3_512:
       return END_OF_FIELD(d.md);
 #else
-    case DIGEST_SHA3_256: /* Fall through */
+    case DIGEST_SHA3_256: FALLTHROUGH;
     case DIGEST_SHA3_512:
       return END_OF_FIELD(d.sha3);
 #endif /* defined(OPENSSL_HAS_SHA3) */
@@ -304,14 +304,14 @@ crypto_digest_add_bytes(crypto_digest_t *digest, const char *data,
       SHA512_Update(&digest->d.sha512, (void*)data, len);
       break;
 #ifdef OPENSSL_HAS_SHA3
-    case DIGEST_SHA3_256: /* FALLSTHROUGH */
+    case DIGEST_SHA3_256: FALLTHROUGH;
     case DIGEST_SHA3_512: {
       int r = EVP_DigestUpdate(digest->d.md, data, len);
       tor_assert(r);
   }
       break;
 #else /* !defined(OPENSSL_HAS_SHA3) */
-    case DIGEST_SHA3_256: /* FALLSTHROUGH */
+    case DIGEST_SHA3_256: FALLTHROUGH;
     case DIGEST_SHA3_512:
       keccak_digest_update(&digest->d.sha3, (const uint8_t *)data, len);
       break;
@@ -377,7 +377,7 @@ crypto_digest_get_digest(crypto_digest_t *digest,
       SHA512_Final(r, &tmpenv.d.sha512);
       break;
 //LCOV_EXCL_START
-    case DIGEST_SHA3_256: /* FALLSTHROUGH */
+    case DIGEST_SHA3_256: FALLTHROUGH;
     case DIGEST_SHA3_512:
     default:
       log_warn(LD_BUG, "Handling unexpected algorithm %d", digest->algorithm);
diff --git a/src/test/test_socks.c b/src/test/test_socks.c
index 40fb0481c6..4a465c7361 100644
--- a/src/test/test_socks.c
+++ b/src/test/test_socks.c
@@ -815,7 +815,7 @@ test_socks_truncated(void *ptr)
   for (i = 0; i < ARRAY_LENGTH(commands); ++i) {
     for (j = 0; j < commands[i].len; ++j) {
       switch (commands[i].setup) {
-        default: /* Falls through */
+        default: FALLTHROUGH;
         case NONE:
           /* This test calls for no setup on the socks state. */
           break;