diff --git a/lib/transfer.c b/lib/transfer.c
index 664a412bdbce0b93ada74cb1696df53c02172e06..11a8f84636ec61e1344cdb7f8b2fab2dd0c02b27 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