diff --git a/mongoose.c b/mongoose.c
index e1871067..b7ceadd4 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -3027,7 +3027,7 @@ SOCKET mg_open_listener(const char *url, struct mg_addr *addr) {
     }
   }
   if (fd == INVALID_SOCKET) {
-    if (s_err = 0) s_err = MG_SOCK_ERRNO;
+    if (s_err == 0) s_err = MG_SOCK_ERRNO;
     LOG(LL_ERROR, ("Failed to listen on %s, errno %d", url, s_err));
   }
 
diff --git a/src/sock.c b/src/sock.c
index 4accc934..028e28f0 100644
--- a/src/sock.c
+++ b/src/sock.c
@@ -181,7 +181,7 @@ SOCKET mg_open_listener(const char *url, struct mg_addr *addr) {
     }
   }
   if (fd == INVALID_SOCKET) {
-    if (s_err = 0) s_err = MG_SOCK_ERRNO;
+    if (s_err == 0) s_err = MG_SOCK_ERRNO;
     LOG(LL_ERROR, ("Failed to listen on %s, errno %d", url, s_err));
   }