diff --git a/gzlib.c b/gzlib.c
index 7a37a96cf0..78702174ca 100644
--- a/gzlib.c
+++ b/gzlib.c
@@ -299,7 +299,7 @@ gzFile ZEXPORT gzdopen(int fd, const char *mode) {
     char *path;         /* identifier for error messages */
     gzFile gz;
 
-    if (fd == -1 || (path = (char *)malloc(7 + 3 * sizeof(int))) == NULL)
+    if (fd < 0 || (path = (char *)malloc(7 + 3 * sizeof(int))) == NULL)
         return NULL;
 #if !defined(NO_snprintf) && !defined(NO_vsnprintf)
     (void)snprintf(path, 7 + 3 * sizeof(int), "<fd:%d>", fd);