diff --git a/a8/websocketsession.cc b/a8/websocketsession.cc
index 14192f1..c3aae61 100644
--- a/a8/websocketsession.cc
+++ b/a8/websocketsession.cc
@@ -196,8 +196,8 @@ namespace a8
         }
         char* real_buf = buf + offset;
         unsigned int ava_len = buflen - offset;
-        char header = real_buf[0];
-        char mask_payloadlen = real_buf[1];
+        unsigned char header = real_buf[0];
+        unsigned char mask_payloadlen = real_buf[1];
 
         bool is_final_frame = (header & FIN) == FIN;
         #if 0