diff --git a/src/core/ngx_conf_file.c b/src/core/ngx_conf_file.c
index 5818636..60d68a0 100644
--- a/src/core/ngx_conf_file.c
+++ b/src/core/ngx_conf_file.c
@@ -741,7 +741,7 @@
     }
 
     bufs->size = ngx_parse_size(&value[2]);
-    if (bufs->size == NGX_ERROR || bufs->size == 0) {
+    if (bufs->size == (size_t) NGX_ERROR || bufs->size == 0) {
         return "invalid value";
     }