diff --git a/src/core/ngx_crc.h b/src/core/ngx_crc.h
index b2aff8966..11bf32824 100644
--- a/src/core/ngx_crc.h
+++ b/src/core/ngx_crc.h
@@ -11,7 +11,7 @@
 /* 32-bit crc16 */
 
 static ngx_inline uint32_t
-ngx_crc(char *data, size_t len)
+ngx_crc(u_char *data, size_t len)
 {
     uint32_t  sum;