diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 4c72a0d43b32..f7118836ea6e 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -65,6 +65,7 @@
 #include "funcapi.h"
 #include "libpq/libpq.h"
 #include "libpq/pqformat.h"
+#include "libpq/protocol.h"
 #include "miscadmin.h"
 #include "nodes/replnodes.h"
 #include "pgstat.h"
@@ -735,13 +736,13 @@ HandleUploadManifestPacket(StringInfo buf, off_t *offset,
 
 	switch (mtype)
 	{
-		case 'd':				/* CopyData */
+		case PqMsg_CopyData:
 			maxmsglen = PQ_LARGE_MESSAGE_LIMIT;
 			break;
-		case 'c':				/* CopyDone */
-		case 'f':				/* CopyFail */
-		case 'H':				/* Flush */
-		case 'S':				/* Sync */
+		case PqMsg_CopyDone:
+		case PqMsg_CopyFail:
+		case PqMsg_Flush:
+		case PqMsg_Sync:
 			maxmsglen = PQ_SMALL_MESSAGE_LIMIT;
 			break;
 		default:
@@ -763,19 +764,19 @@ HandleUploadManifestPacket(StringInfo buf, off_t *offset,
 	/* Process the message */
 	switch (mtype)
 	{
-		case 'd':				/* CopyData */
+		case PqMsg_CopyData:
 			AppendIncrementalManifestData(ib, buf->data, buf->len);
 			return true;
 
-		case 'c':				/* CopyDone */
+		case PqMsg_CopyDone:
 			return false;
 
-		case 'H':				/* Sync */
-		case 'S':				/* Flush */
+		case PqMsg_Sync:
+		case PqMsg_Flush:
 			/* Ignore these while in CopyOut mode as we do elsewhere. */
 			return true;
 
-		case 'f':
+		case PqMsg_CopyFail:
 			ereport(ERROR,
 					(errcode(ERRCODE_QUERY_CANCELED),
 					 errmsg("COPY from stdin failed: %s",
@@ -2305,7 +2306,7 @@ ProcessRepliesIfAny(void)
 			case PqMsg_CopyDone:
 				if (!streamingDoneSending)
 				{
-					pq_putmessage_noblock('c', NULL, 0);
+					pq_putmessage_noblock(PqMsg_CopyDone, NULL, 0);
 					streamingDoneSending = true;
 				}
 
@@ -3306,7 +3307,7 @@ XLogSendPhysical(void)
 			wal_segment_close(xlogreader);
 
 		/* Send CopyDone */
-		pq_putmessage_noblock('c', NULL, 0);
+		pq_putmessage_noblock(PqMsg_CopyDone, NULL, 0);
 		streamingDoneSending = true;
 
 		WalSndCaughtUp = true;