diff --git a/cmdutils.c b/cmdutils.c
index 3ae48e4863..ac971df20a 100644
--- a/cmdutils.c
+++ b/cmdutils.c
@@ -1061,7 +1061,7 @@ int cmdutils_read_file(const char *filename, char **bufptr, size_t *size)
             ret = AVERROR_EOF;
     } else {
         ret = 0;
-        (*bufptr)[*size++] = '\0';
+        (*bufptr)[(*size)++] = '\0';
     }
 
     fclose(f);