diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
index 0d8a66aa9f0..2005674838d 100644
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -3077,6 +3077,11 @@ lmerge_matched:
 							   *inputslot;
 					LockTupleMode lockmode;
 
+					if (IsolationUsesXactSnapshot())
+						ereport(ERROR,
+								(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
+								 errmsg("could not serialize access due to concurrent update")));
+
 					/*
 					 * The target tuple was concurrently updated by some other
 					 * transaction. Run EvalPlanQual() with the new version of
diff --git a/src/test/isolation/expected/merge-update.out b/src/test/isolation/expected/merge-update.out
index f5f7e3ba19b..5170f6ee019 100644
--- a/src/test/isolation/expected/merge-update.out
+++ b/src/test/isolation/expected/merge-update.out
@@ -355,3 +355,28 @@ step c1: COMMIT;
 step pa_merge2c_dup: <... completed>
 ERROR:  MERGE command cannot affect row a second time
 step a2: ABORT;
+
+starting permutation: merge2a c1 s1beginrr merge1 c2
+step merge2a: 
+  MERGE INTO target t
+  USING (SELECT 1 as key, 'merge2a' as val) s
+  ON s.key = t.key
+  WHEN NOT MATCHED THEN
+	INSERT VALUES (s.key, s.val)
+  WHEN MATCHED THEN
+	UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+
+step c1: COMMIT;
+step s1beginrr: BEGIN ISOLATION LEVEL REPEATABLE READ;
+step merge1: 
+  MERGE INTO target t
+  USING (SELECT 1 as key, 'merge1' as val) s
+  ON s.key = t.key
+  WHEN NOT MATCHED THEN
+	INSERT VALUES (s.key, s.val)
+  WHEN MATCHED THEN
+    UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+ <waiting ...>
+step c2: COMMIT;
+step merge1: <... completed>
+ERROR:  could not serialize access due to concurrent update
diff --git a/src/test/isolation/specs/merge-update.spec b/src/test/isolation/specs/merge-update.spec
index 3ccd4664498..293cdb46b56 100644
--- a/src/test/isolation/specs/merge-update.spec
+++ b/src/test/isolation/specs/merge-update.spec
@@ -78,6 +78,7 @@ step "pa_merge3"
 }
 step "c1" { COMMIT; }
 step "a1" { ABORT; }
+step "s1beginrr" { BEGIN ISOLATION LEVEL REPEATABLE READ; }
 
 session "s2"
 setup
@@ -167,3 +168,4 @@ permutation "pa_merge2" "c1" "pa_merge2a" "pa_select2" "c2" # succeeds
 permutation "pa_merge3" "pa_merge2b_when" "c1" "pa_select2" "c2" # WHEN not satisfied by updated tuple
 permutation "pa_merge1" "pa_merge2b_when" "c1" "pa_select2" "c2" # WHEN satisfied by updated tuple
 permutation "pa_merge1" "pa_merge2c_dup" "c1" "a2"
+permutation "merge2a" "c1" "s1beginrr" "merge1" "c2"