diff --git a/changes/bug40190 b/changes/bug40190
new file mode 100644
index 0000000000..0f3d6941dc
--- /dev/null
+++ b/changes/bug40190
@@ -0,0 +1,4 @@
+  o Minor bugfixes (SOCKS5):
+    - Handle partial socks5 messages correctly.  Previously, our code would
+      send an incorrect error message if it got a socks5 request that wasn't
+      complete. Fixes bug 40190; bugfix on 0.3.5.1-alpha.
diff --git a/src/core/proto/proto_socks.c b/src/core/proto/proto_socks.c
index 4f39d69d62..0990014884 100644
--- a/src/core/proto/proto_socks.c
+++ b/src/core/proto/proto_socks.c
@@ -550,6 +550,7 @@ parse_socks5_client_request(const uint8_t *raw_data, socks_request_t *req,
   if (parsed == -1) {
     log_warn(LD_APP, "socks5: parsing failed - invalid client request");
     res = SOCKS_RESULT_INVALID;
+    socks_request_set_socks5_error(req, SOCKS5_GENERAL_ERROR);
     goto end;
   } else if (parsed == -2) {
     res = SOCKS_RESULT_TRUNCATED;
@@ -561,6 +562,7 @@ parse_socks5_client_request(const uint8_t *raw_data, socks_request_t *req,
 
   if (socks5_client_request_get_version(trunnel_req) != 5) {
     res = SOCKS_RESULT_INVALID;
+    socks_request_set_socks5_error(req, SOCKS5_GENERAL_ERROR);
     goto end;
   }
 
@@ -595,6 +597,7 @@ parse_socks5_client_request(const uint8_t *raw_data, socks_request_t *req,
       tor_addr_to_str(req->address, &destaddr, sizeof(req->address), 1);
     } break;
     default: {
+      socks_request_set_socks5_error(req, SOCKS5_ADDRESS_TYPE_NOT_SUPPORTED);
       res = -1;
     } break;
   }
@@ -775,8 +778,10 @@ handle_socks_message(const uint8_t *raw_data, size_t datalen,
     } else {
       res = parse_socks5_client_request(raw_data, req,
                                         datalen, drain_out);
-      if (res != SOCKS_RESULT_DONE) {
+      if (BUG(res == SOCKS_RESULT_INVALID && req->replylen == 0)) {
         socks_request_set_socks5_error(req, SOCKS5_GENERAL_ERROR);
+      }
+      if (res != SOCKS_RESULT_DONE) {
         goto end;
       }