diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c
index 07ae7a31db5..c3998719405 100644
--- a/src/backend/access/transam/multixact.c
+++ b/src/backend/access/transam/multixact.c
@@ -1713,7 +1713,7 @@ PostPrepare_MultiXact(TransactionId xid)
 	myOldestMember = OldestMemberMXactId[MyBackendId];
 	if (MultiXactIdIsValid(myOldestMember))
 	{
-		BackendId	dummyBackendId = TwoPhaseGetDummyBackendId(xid);
+		BackendId	dummyBackendId = TwoPhaseGetDummyBackendId(xid, false);
 
 		/*
 		 * Even though storing MultiXactId is atomic, acquire lock to make
@@ -1755,7 +1755,7 @@ void
 multixact_twophase_recover(TransactionId xid, uint16 info,
 						   void *recdata, uint32 len)
 {
-	BackendId	dummyBackendId = TwoPhaseGetDummyBackendId(xid);
+	BackendId	dummyBackendId = TwoPhaseGetDummyBackendId(xid, false);
 	MultiXactId oldestMember;
 
 	/*
@@ -1776,7 +1776,7 @@ void
 multixact_twophase_postcommit(TransactionId xid, uint16 info,
 							  void *recdata, uint32 len)
 {
-	BackendId	dummyBackendId = TwoPhaseGetDummyBackendId(xid);
+	BackendId	dummyBackendId = TwoPhaseGetDummyBackendId(xid, true);
 
 	Assert(len == sizeof(MultiXactId));
 
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index add979bf0b2..64679dd2de9 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -801,9 +801,12 @@ pg_prepared_xact(PG_FUNCTION_ARGS)
  * TwoPhaseGetGXact
  *		Get the GlobalTransaction struct for a prepared transaction
  *		specified by XID
+ *
+ * If lock_held is set to true, TwoPhaseStateLock will not be taken, so the
+ * caller had better hold it.
  */
 static GlobalTransaction
-TwoPhaseGetGXact(TransactionId xid)
+TwoPhaseGetGXact(TransactionId xid, bool lock_held)
 {
 	GlobalTransaction result = NULL;
 	int			i;
@@ -811,6 +814,8 @@ TwoPhaseGetGXact(TransactionId xid)
 	static TransactionId cached_xid = InvalidTransactionId;
 	static GlobalTransaction cached_gxact = NULL;
 
+	Assert(!lock_held || LWLockHeldByMe(TwoPhaseStateLock));
+
 	/*
 	 * During a recovery, COMMIT PREPARED, or ABORT PREPARED, we'll be called
 	 * repeatedly for the same XID.  We can save work with a simple cache.
@@ -818,7 +823,8 @@ TwoPhaseGetGXact(TransactionId xid)
 	if (xid == cached_xid)
 		return cached_gxact;
 
-	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
+	if (!lock_held)
+		LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
 
 	for (i = 0; i < TwoPhaseState->numPrepXacts; i++)
 	{
@@ -832,7 +838,8 @@ TwoPhaseGetGXact(TransactionId xid)
 		}
 	}
 
-	LWLockRelease(TwoPhaseStateLock);
+	if (!lock_held)
+		LWLockRelease(TwoPhaseStateLock);
 
 	if (result == NULL)			/* should not happen */
 		elog(ERROR, "failed to find GlobalTransaction for xid %u", xid);
@@ -849,12 +856,13 @@ TwoPhaseGetGXact(TransactionId xid)
  *
  * Dummy backend IDs are similar to real backend IDs of real backends.
  * They start at MaxBackends + 1, and are unique across all currently active
- * real backends and prepared transactions.
+ * real backends and prepared transactions.  If lock_held is set to true,
+ * TwoPhaseStateLock will not be taken, so the caller had better hold it.
  */
 BackendId
-TwoPhaseGetDummyBackendId(TransactionId xid)
+TwoPhaseGetDummyBackendId(TransactionId xid, bool lock_held)
 {
-	GlobalTransaction gxact = TwoPhaseGetGXact(xid);
+	GlobalTransaction gxact = TwoPhaseGetGXact(xid, lock_held);
 
 	return gxact->dummyBackendId;
 }
@@ -862,11 +870,14 @@ TwoPhaseGetDummyBackendId(TransactionId xid)
 /*
  * TwoPhaseGetDummyProc
  *		Get the PGPROC that represents a prepared transaction specified by XID
+ *
+ * If lock_held is set to true, TwoPhaseStateLock will not be taken, so the
+ * caller had better hold it.
  */
 PGPROC *
-TwoPhaseGetDummyProc(TransactionId xid)
+TwoPhaseGetDummyProc(TransactionId xid, bool lock_held)
 {
-	GlobalTransaction gxact = TwoPhaseGetGXact(xid);
+	GlobalTransaction gxact = TwoPhaseGetGXact(xid, lock_held);
 
 	return &ProcGlobal->allProcs[gxact->pgprocno];
 }
@@ -1560,6 +1571,14 @@ FinishPreparedTransaction(const char *gid, bool isCommit)
 	if (hdr->initfileinval)
 		RelationCacheInitFilePostInvalidate();
 
+	/*
+	 * Acquire the two-phase lock.  We want to work on the two-phase callbacks
+	 * while holding it to avoid potential conflicts with other transactions
+	 * attempting to use the same GID, so the lock is released once the shared
+	 * memory state is cleared.
+	 */
+	LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
+
 	/* And now do the callbacks */
 	if (isCommit)
 		ProcessRecords(bufptr, xid, twophase_postcommit_callbacks);
@@ -1568,6 +1587,15 @@ FinishPreparedTransaction(const char *gid, bool isCommit)
 
 	PredicateLockTwoPhaseFinish(xid, isCommit);
 
+	/* Clear shared memory state */
+	RemoveGXact(gxact);
+
+	/*
+	 * Release the lock as all callbacks are called and shared memory cleanup
+	 * is done.
+	 */
+	LWLockRelease(TwoPhaseStateLock);
+
 	/* Count the prepared xact as committed or aborted */
 	AtEOXact_PgStat(isCommit);
 
@@ -1577,9 +1605,6 @@ FinishPreparedTransaction(const char *gid, bool isCommit)
 	if (gxact->ondisk)
 		RemoveTwoPhaseFile(xid, true);
 
-	LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
-	RemoveGXact(gxact);
-	LWLockRelease(TwoPhaseStateLock);
 	MyLockedGxact = NULL;
 
 	RESUME_INTERRUPTS();
diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c
index 3bb5ce350aa..78fdbd6ff88 100644
--- a/src/backend/storage/lmgr/lock.c
+++ b/src/backend/storage/lmgr/lock.c
@@ -3243,7 +3243,7 @@ AtPrepare_Locks(void)
 void
 PostPrepare_Locks(TransactionId xid)
 {
-	PGPROC	   *newproc = TwoPhaseGetDummyProc(xid);
+	PGPROC	   *newproc = TwoPhaseGetDummyProc(xid, false);
 	HASH_SEQ_STATUS status;
 	LOCALLOCK  *locallock;
 	LOCK	   *lock;
@@ -4034,7 +4034,7 @@ lock_twophase_recover(TransactionId xid, uint16 info,
 					  void *recdata, uint32 len)
 {
 	TwoPhaseLockRecord *rec = (TwoPhaseLockRecord *) recdata;
-	PGPROC	   *proc = TwoPhaseGetDummyProc(xid);
+	PGPROC	   *proc = TwoPhaseGetDummyProc(xid, false);
 	LOCKTAG    *locktag;
 	LOCKMODE	lockmode;
 	LOCKMETHODID lockmethodid;
@@ -4247,7 +4247,7 @@ lock_twophase_postcommit(TransactionId xid, uint16 info,
 						 void *recdata, uint32 len)
 {
 	TwoPhaseLockRecord *rec = (TwoPhaseLockRecord *) recdata;
-	PGPROC	   *proc = TwoPhaseGetDummyProc(xid);
+	PGPROC	   *proc = TwoPhaseGetDummyProc(xid, true);
 	LOCKTAG    *locktag;
 	LOCKMETHODID lockmethodid;
 	LockMethod	lockMethodTable;
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index 6228b091d89..fcd1913c43a 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -34,8 +34,8 @@ extern void TwoPhaseShmemInit(void);
 extern void AtAbort_Twophase(void);
 extern void PostPrepare_Twophase(void);
 
-extern PGPROC *TwoPhaseGetDummyProc(TransactionId xid);
-extern BackendId TwoPhaseGetDummyBackendId(TransactionId xid);
+extern PGPROC *TwoPhaseGetDummyProc(TransactionId xid, bool lock_held);
+extern BackendId TwoPhaseGetDummyBackendId(TransactionId xid, bool lock_held);
 
 extern GlobalTransaction MarkAsPreparing(TransactionId xid, const char *gid,
 				TimestampTz prepared_at,