diff --git a/lib/transfer.c b/lib/transfer.c
index 664a412bd..11a8f8463 100644
--- a/lib/transfer.c
+++ b/lib/transfer.c
@@ -2223,7 +2223,7 @@ CURLcode Curl_perform(struct SessionHandle *data)
      * an error, use the strerror() string or if things are so bad that not
      * even that is good, set a bad string that mentions the error code.
      */
-    char *str = curl_easy_strerror(res);
+    const char *str = curl_easy_strerror(res);
     if(!str)
       failf(data, "unspecified error %d", (int)res);
     else