diff --git a/ares/ares__read_line.c b/ares/ares__read_line.c
index 9f8445ad3..d816f18c0 100644
--- a/ares/ares__read_line.c
+++ b/ares/ares__read_line.c
@@ -30,7 +30,8 @@
 int ares__read_line(FILE *fp, char **buf, int *bufsize)
 {
   char *newbuf;
-  int offset = 0, len;
+  int offset = 0;
+  size_t len;
 
   if (*buf == NULL)
     {