diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 96dc923..3ebe799 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -11050,12 +11050,20 @@ ATExecReplicaIdentity(Relation rel, ReplicaIdentityStmt *stmt, LOCKMODE lockmode
 		int16		attno = indexRel->rd_index->indkey.values[key];
 		Form_pg_attribute attr;
 
-		/* Of the system columns, only oid is indexable. */
-		if (attno <= 0 && attno != ObjectIdAttributeNumber)
-			elog(ERROR, "internal column %u in unique index \"%s\"",
-				 attno, RelationGetRelationName(indexRel));
+		/* Allow OIDs to be indexed. No need to check for nullabiliy here */
+		if (attno == ObjectIdAttributeNumber)
+			continue;
+
+		/* Reject any other system columns */
+		if (attno <= 0)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
+					 errmsg("index \"%s\" cannot be used as replica identity because column %d is a system column",
+							RelationGetRelationName(indexRel), attno)));
 
 		attr = rel->rd_att->attrs[attno - 1];
+
+		/* Must be a non-system column. Check it's not nullable */
 		if (!attr->attnotnull)
 			ereport(ERROR,
 					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
diff --git a/src/test/regress/expected/replica_identity.out b/src/test/regress/expected/replica_identity.out
index 60d9a42..47678db 100644
--- a/src/test/regress/expected/replica_identity.out
+++ b/src/test/regress/expected/replica_identity.out
@@ -9,6 +9,7 @@ CREATE TABLE test_replica_identity (
 CREATE TABLE test_replica_identity_othertable (id serial primary key);
 CREATE INDEX test_replica_identity_keyab ON test_replica_identity (keya, keyb);
 CREATE UNIQUE INDEX test_replica_identity_keyab_key ON test_replica_identity (keya, keyb);
+CREATE UNIQUE INDEX test_replica_indentity_syscol ON test_replica_identity (ctid);
 CREATE UNIQUE INDEX test_replica_identity_nonkey ON test_replica_identity (keya, nonkey);
 CREATE INDEX test_replica_identity_hash ON test_replica_identity USING hash (nonkey);
 WARNING:  hash indexes are not WAL-logged and their use is discouraged
@@ -40,6 +41,9 @@ SELECT relreplident FROM pg_class WHERE oid = 'pg_constraint'::regclass;
 -- fail, not unique
 ALTER TABLE test_replica_identity REPLICA IDENTITY USING INDEX test_replica_identity_keyab;
 ERROR:  cannot use non-unique index "test_replica_identity_keyab" as replica identity
+-- fail, index can't contain system columns
+ALTER TABLE test_replica_identity REPLICA IDENTITY USING INDEX test_replica_indentity_syscol;
+ERROR:  index "test_replica_indentity_syscol" cannot be used as replica identity because column -1 is a system column
 -- fail, not a candidate key, nullable column
 ALTER TABLE test_replica_identity REPLICA IDENTITY USING INDEX test_replica_identity_nonkey;
 ERROR:  index "test_replica_identity_nonkey" cannot be used as replica identity because column "nonkey" is nullable
@@ -91,6 +95,7 @@ Indexes:
     "test_replica_identity_partial" UNIQUE, btree (keya, keyb) WHERE keyb <> '3'::text
     "test_replica_identity_unique_defer" UNIQUE CONSTRAINT, btree (keya, keyb) DEFERRABLE
     "test_replica_identity_unique_nondefer" UNIQUE CONSTRAINT, btree (keya, keyb)
+    "test_replica_indentity_syscol" UNIQUE, btree (ctid)
     "test_replica_identity_hash" hash (nonkey)
     "test_replica_identity_keyab" btree (keya, keyb)
 
@@ -121,6 +126,7 @@ Indexes:
     "test_replica_identity_partial" UNIQUE, btree (keya, keyb) WHERE keyb <> '3'::text
     "test_replica_identity_unique_defer" UNIQUE CONSTRAINT, btree (keya, keyb) DEFERRABLE
     "test_replica_identity_unique_nondefer" UNIQUE CONSTRAINT, btree (keya, keyb)
+    "test_replica_indentity_syscol" UNIQUE, btree (ctid)
     "test_replica_identity_hash" hash (nonkey)
     "test_replica_identity_keyab" btree (keya, keyb)
 
@@ -169,6 +175,7 @@ Indexes:
     "test_replica_identity_partial" UNIQUE, btree (keya, keyb) WHERE keyb <> '3'::text
     "test_replica_identity_unique_defer" UNIQUE CONSTRAINT, btree (keya, keyb) DEFERRABLE
     "test_replica_identity_unique_nondefer" UNIQUE CONSTRAINT, btree (keya, keyb)
+    "test_replica_indentity_syscol" UNIQUE, btree (ctid)
     "test_replica_identity_hash" hash (nonkey)
     "test_replica_identity_keyab" btree (keya, keyb)
 Replica Identity: FULL
diff --git a/src/test/regress/sql/replica_identity.sql b/src/test/regress/sql/replica_identity.sql
index 20b6826..436851c 100644
--- a/src/test/regress/sql/replica_identity.sql
+++ b/src/test/regress/sql/replica_identity.sql
@@ -11,6 +11,7 @@ CREATE TABLE test_replica_identity_othertable (id serial primary key);
 
 CREATE INDEX test_replica_identity_keyab ON test_replica_identity (keya, keyb);
 CREATE UNIQUE INDEX test_replica_identity_keyab_key ON test_replica_identity (keya, keyb);
+CREATE UNIQUE INDEX test_replica_indentity_syscol ON test_replica_identity (ctid);
 CREATE UNIQUE INDEX test_replica_identity_nonkey ON test_replica_identity (keya, nonkey);
 CREATE INDEX test_replica_identity_hash ON test_replica_identity USING hash (nonkey);
 CREATE UNIQUE INDEX test_replica_identity_expr ON test_replica_identity (keya, keyb, (3));
@@ -28,6 +29,8 @@ SELECT relreplident FROM pg_class WHERE oid = 'pg_constraint'::regclass;
 
 -- fail, not unique
 ALTER TABLE test_replica_identity REPLICA IDENTITY USING INDEX test_replica_identity_keyab;
+-- fail, index can't contain system columns
+ALTER TABLE test_replica_identity REPLICA IDENTITY USING INDEX test_replica_indentity_syscol;
 -- fail, not a candidate key, nullable column
 ALTER TABLE test_replica_identity REPLICA IDENTITY USING INDEX test_replica_identity_nonkey;
 -- fail, hash indexes cannot do uniqueness