diff --git a/http-auth.c b/http-auth.c
index 1085947..c41d77b 100644
--- a/http-auth.c
+++ b/http-auth.c
@@ -178,7 +178,7 @@ char* digest_authentication_encode(const char *line, const char *user, const cha
 		return NULL;
 	}
 
-	if (qop && strncasecmp(qop, "auth", 4) != 0) {
+	if (qop && strncasecmp(qop, "auth", 5) != 0) {
 		/* FIXME: currently don't support auth-int */
 		free(realm);
 		free(opaque);