diff --git a/pngrutil.c b/pngrutil.c
index d543091..2f6d6ad 100644
--- a/pngrutil.c
+++ b/pngrutil.c
@@ -2174,7 +2174,7 @@
    /* We need to have at least 12 bytes after the purpose string
     * in order to get the parameter information.
     */
-   if (endptr - buf <= 12U)
+   if (endptr - buf <= 12)
    {
       png_chunk_benign_error(png_ptr, "invalid");
       return;