diff --git a/src/common/crypto_ed25519.c b/src/common/crypto_ed25519.c
index 599a1ca9b7..1606d02c48 100644
--- a/src/common/crypto_ed25519.c
+++ b/src/common/crypto_ed25519.c
@@ -381,10 +381,13 @@ ed25519_seckey_read_from_file(ed25519_secret_key_t *seckey_out,
   len = crypto_read_tagged_contents_from_file(filename, "ed25519v1-secret",
                                               tag_out, seckey_out->seckey,
                                               sizeof(seckey_out->seckey));
-  if (len != sizeof(seckey_out->seckey))
-    return -1;
+  if (len == sizeof(seckey_out->seckey)) {
+    return 0;
+  } else if (len >= 0) {
+    errno = EINVAL;
+  }
 
-  return 0;
+  return -1;
 }
 
 /**
@@ -417,10 +420,13 @@ ed25519_pubkey_read_from_file(ed25519_public_key_t *pubkey_out,
   len = crypto_read_tagged_contents_from_file(filename, "ed25519v1-public",
                                               tag_out, pubkey_out->pubkey,
                                               sizeof(pubkey_out->pubkey));
-  if (len != sizeof(pubkey_out->pubkey))
-    return -1;
+  if (len == sizeof(pubkey_out->pubkey)) {
+    return 0;
+  } else if (len >= 0) {
+    errno = EINVAL;
+  }
 
-  return 0;
+  return -1;
 }
 
 /** Release all storage held for <b>kp</b>. */
diff --git a/src/common/util.c b/src/common/util.c
index a140057dea..1849613512 100644
--- a/src/common/util.c
+++ b/src/common/util.c
@@ -1997,8 +1997,10 @@ read_all(tor_socket_t fd, char *buf, size_t count, int isSocket)
   size_t numread = 0;
   ssize_t result;
 
-  if (count > SIZE_T_CEILING || count > SSIZE_MAX)
+  if (count > SIZE_T_CEILING || count > SSIZE_MAX) {
+    errno = EINVAL;
     return -1;
+  }
 
   while (numread != count) {
     if (isSocket)
@@ -2558,8 +2560,10 @@ read_file_to_str_until_eof(int fd, size_t max_bytes_to_read, size_t *sz_out)
   char *string = NULL;
   size_t string_max = 0;
 
-  if (max_bytes_to_read+1 >= SIZE_T_CEILING)
+  if (max_bytes_to_read+1 >= SIZE_T_CEILING) {
+    errno = EINVAL; 
     return NULL;
+  }
 
   do {
     /* XXXX This "add 1K" approach is a little goofy; if we care about
@@ -2655,6 +2659,7 @@ read_file_to_str(const char *filename, int flags, struct stat *stat_out)
 
   if ((uint64_t)(statbuf.st_size)+1 >= SIZE_T_CEILING) {
     close(fd);
+    errno = EINVAL;
     return NULL;
   }
 
diff --git a/src/or/routerkeys.c b/src/or/routerkeys.c
index 946c48bc08..77bbcfd49f 100644
--- a/src/or/routerkeys.c
+++ b/src/or/routerkeys.c
@@ -34,14 +34,18 @@ read_encrypted_secret_key(ed25519_secret_key_t *out,
     r = 0;
     goto done;
   }
-  if (strcmp(tag, ENC_KEY_TAG))
+  if (strcmp(tag, ENC_KEY_TAG)) {
+    saved_errno = EINVAL;
     goto done;
+  }
 
   while (1) {
     ssize_t pwlen =
       tor_getpass("Enter pasphrase for master key:", pwbuf, sizeof(pwbuf));
-    if (pwlen < 0)
+    if (pwlen < 0) {
+      saved_errno = EINVAL;
       goto done;
+    }
 
     const int r = crypto_unpwbox(&secret, &secret_len,
                                  encrypted_key, encrypted_len,