diff --git a/src/shrpx_memcached_connection.cc b/src/shrpx_memcached_connection.cc
index 775ef9e9..fbae2bbd 100644
--- a/src/shrpx_memcached_connection.cc
+++ b/src/shrpx_memcached_connection.cc
@@ -445,7 +445,7 @@ int MemcachedConnection::parse_packet() {
       }
       ++in;
 
-      parse_state_.op = *in++;
+      parse_state_.op = static_cast<MemcachedOp>(*in++);
       parse_state_.keylen = util::get_uint16(in);
       in += 2;
       parse_state_.extralen = *in++;
@@ -463,7 +463,8 @@ int MemcachedConnection::parse_packet() {
       if (req->op != parse_state_.op) {
         MCLOG(WARN, this)
             << "opcode in response does not match to the request: want "
-            << static_cast<uint32_t>(req->op) << ", got " << parse_state_.op;
+            << static_cast<uint32_t>(req->op) << ", got "
+            << static_cast<uint32_t>(parse_state_.op);
         return -1;
       }
 
@@ -479,7 +480,7 @@ int MemcachedConnection::parse_packet() {
         return -1;
       }
 
-      if (parse_state_.op == MEMCACHED_OP_GET &&
+      if (parse_state_.op == MemcachedOp::GET &&
           parse_state_.status_code == 0 && parse_state_.extralen == 0) {
         MCLOG(WARN, this) << "response for GET does not have extra";
         return -1;
@@ -661,9 +662,9 @@ void MemcachedConnection::drain_send_queue(size_t nwrite) {
 
 size_t MemcachedConnection::serialized_size(MemcachedRequest *req) {
   switch (req->op) {
-  case MEMCACHED_OP_GET:
+  case MemcachedOp::GET:
     return 24 + req->key.size();
-  case MEMCACHED_OP_ADD:
+  case MemcachedOp::ADD:
   default:
     return 24 + 8 + req->key.size() + req->value.size();
   }
@@ -676,14 +677,14 @@ void MemcachedConnection::make_request(MemcachedSendbuf *sendbuf,
   std::fill(std::begin(headbuf.buf), std::end(headbuf.buf), 0);
 
   headbuf[0] = MEMCACHED_REQ_MAGIC;
-  headbuf[1] = req->op;
+  headbuf[1] = static_cast<uint8_t>(req->op);
   switch (req->op) {
-  case MEMCACHED_OP_GET:
+  case MemcachedOp::GET:
     util::put_uint16be(&headbuf[2], req->key.size());
     util::put_uint32be(&headbuf[8], req->key.size());
     headbuf.write(24);
     break;
-  case MEMCACHED_OP_ADD:
+  case MemcachedOp::ADD:
     util::put_uint16be(&headbuf[2], req->key.size());
     headbuf[4] = 8;
     util::put_uint32be(&headbuf[8], 8 + req->key.size() + req->value.size());
diff --git a/src/shrpx_memcached_connection.h b/src/shrpx_memcached_connection.h
index 4702f56d..aff76044 100644
--- a/src/shrpx_memcached_connection.h
+++ b/src/shrpx_memcached_connection.h
@@ -43,6 +43,7 @@ using namespace nghttp2;
 namespace shrpx {
 
 struct MemcachedRequest;
+enum class MemcachedOp : uint8_t;
 
 enum class MemcachedParseState {
   HEADER24,
@@ -70,7 +71,7 @@ struct MemcachedParseContext {
   // status_code in response
   int status_code;
   // op in response
-  int op;
+  MemcachedOp op;
 };
 
 struct MemcachedSendbuf {
diff --git a/src/shrpx_memcached_request.h b/src/shrpx_memcached_request.h
index 3bd79fd7..36969831 100644
--- a/src/shrpx_memcached_request.h
+++ b/src/shrpx_memcached_request.h
@@ -35,9 +35,9 @@
 
 namespace shrpx {
 
-enum {
-  MEMCACHED_OP_GET = 0x00,
-  MEMCACHED_OP_ADD = 0x02,
+enum class MemcachedOp : uint8_t {
+  GET = 0x00,
+  ADD = 0x02,
 };
 
 struct MemcachedRequest;
@@ -50,7 +50,7 @@ struct MemcachedRequest {
   std::vector<uint8_t> value;
   MemcachedResultCallback cb;
   uint32_t expiry;
-  int op;
+  MemcachedOp op;
   bool canceled;
 };
 
diff --git a/src/shrpx_tls.cc b/src/shrpx_tls.cc
index a5821e8a..83d89e67 100644
--- a/src/shrpx_tls.cc
+++ b/src/shrpx_tls.cc
@@ -330,7 +330,7 @@ int tls_session_new_cb(SSL *ssl, SSL_SESSION *session) {
   }
 
   auto req = std::make_unique<MemcachedRequest>();
-  req->op = MEMCACHED_OP_ADD;
+  req->op = MemcachedOp::ADD;
   req->key = MEMCACHED_SESSION_CACHE_KEY_PREFIX.str();
   req->key +=
       util::format_hex(balloc, StringRef{id, static_cast<size_t>(idlen)});
@@ -398,7 +398,7 @@ SSL_SESSION *tls_session_get_cb(SSL *ssl,
   }
 
   auto req = std::make_unique<MemcachedRequest>();
-  req->op = MEMCACHED_OP_GET;
+  req->op = MemcachedOp::GET;
   req->key = MEMCACHED_SESSION_CACHE_KEY_PREFIX.str();
   req->key +=
       util::format_hex(balloc, StringRef{id, static_cast<size_t>(idlen)});
diff --git a/src/shrpx_worker_process.cc b/src/shrpx_worker_process.cc
index 7ed8449e..6af4563a 100644
--- a/src/shrpx_worker_process.cc
+++ b/src/shrpx_worker_process.cc
@@ -272,7 +272,7 @@ void memcached_get_ticket_key_cb(struct ev_loop *loop, ev_timer *w,
 
   auto req = std::make_unique<MemcachedRequest>();
   req->key = "nghttpx:tls-ticket-key";
-  req->op = MEMCACHED_OP_GET;
+  req->op = MemcachedOp::GET;
   req->cb = [conn_handler, w](MemcachedRequest *req, MemcachedResult res) {
     switch (res.status_code) {
     case MEMCACHED_ERR_NO_ERROR: