diff --git a/block/curl.c b/block/curl.c
index 419df78258..684c677ef7 100644
--- a/block/curl.c
+++ b/block/curl.c
@@ -871,8 +871,8 @@ static int curl_open(BlockDriverState *bs, QDict *options, int flags,
         goto out;
     }
 
-    if ((!strncasecmp(s->url, "http://", strlen("http://"))
-        || !strncasecmp(s->url, "https://", strlen("https://")))
+    if ((!g_ascii_strncasecmp(s->url, "http://", strlen("http://"))
+        || !g_ascii_strncasecmp(s->url, "https://", strlen("https://")))
         && !s->accept_range) {
         pstrcpy(state->errmsg, CURL_ERROR_SIZE,
                 "Server does not support 'range' (byte ranges).");