diff --git a/src/shrpx_client_handler.cc b/src/shrpx_client_handler.cc
index 6985e079..1ecfbbe7 100644
--- a/src/shrpx_client_handler.cc
+++ b/src/shrpx_client_handler.cc
@@ -519,7 +519,7 @@ void ClientHandler::signal_reset_upstream_conn_rtimer() {
 
 int ClientHandler::validate_next_proto() {
   const unsigned char *next_proto = nullptr;
-  unsigned int next_proto_len;
+  unsigned int next_proto_len = 0;
 
   // First set callback for catch all cases
   on_read_ = &ClientHandler::upstream_read;
diff --git a/src/shrpx_http2_session.cc b/src/shrpx_http2_session.cc
index 8527aa53..28bd34b2 100644
--- a/src/shrpx_http2_session.cc
+++ b/src/shrpx_http2_session.cc
@@ -1424,7 +1424,7 @@ int Http2Session::connection_made() {
 
   if (ssl_ctx_) {
     const unsigned char *next_proto = nullptr;
-    unsigned int next_proto_len;
+    unsigned int next_proto_len = 0;
     SSL_get0_next_proto_negotiated(conn_.tls.ssl, &next_proto, &next_proto_len);
     for (int i = 0; i < 2; ++i) {
       if (next_proto) {