diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index e8aafbac50..3e24800fbd 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -4786,8 +4786,8 @@ Size
 EstimateTransactionStateSpace(void)
 {
 	TransactionState s;
-	Size		nxids = 5;		/* iso level, deferrable, top & current XID,
-								 * XID count */
+	Size		nxids = 6;		/* iso level, deferrable, top & current XID,
+								 * command counter, XID count */
 
 	for (s = CurrentTransactionState; s != NULL; s = s->parent)
 	{
@@ -4807,12 +4807,13 @@ EstimateTransactionStateSpace(void)
  *
  * We need to save and restore XactDeferrable, XactIsoLevel, and the XIDs
  * associated with this transaction.  The first eight bytes of the result
- * contain XactDeferrable and XactIsoLevel; the next eight bytes contain the
- * XID of the top-level transaction and the XID of the current transaction
- * (or, in each case, InvalidTransactionId if none).  After that, the next 4
- * bytes contain a count of how many additional XIDs follow; this is followed
- * by all of those XIDs one after another.  We emit the XIDs in sorted order
- * for the convenience of the receiving process.
+ * contain XactDeferrable and XactIsoLevel; the next twelve bytes contain the
+ * XID of the top-level transaction, the XID of the current transaction
+ * (or, in each case, InvalidTransactionId if none), and the current command
+ * counter.  After that, the next 4 bytes contain a count of how many
+ * additional XIDs follow; this is followed by all of those XIDs one after
+ * another.  We emit the XIDs in sorted order for the convenience of the
+ * receiving process.
  */
 void
 SerializeTransactionState(Size maxsize, char *start_address)
@@ -4820,14 +4821,16 @@ SerializeTransactionState(Size maxsize, char *start_address)
 	TransactionState s;
 	Size		nxids = 0;
 	Size		i = 0;
+	Size		c = 0;
 	TransactionId *workspace;
 	TransactionId *result = (TransactionId *) start_address;
 
-	Assert(maxsize >= 5 * sizeof(TransactionId));
-	result[0] = (TransactionId) XactIsoLevel;
-	result[1] = (TransactionId) XactDeferrable;
-	result[2] = XactTopTransactionId;
-	result[3] = CurrentTransactionState->transactionId;
+	result[c++] = (TransactionId) XactIsoLevel;
+	result[c++] = (TransactionId) XactDeferrable;
+	result[c++] = XactTopTransactionId;
+	result[c++] = CurrentTransactionState->transactionId;
+	result[c++] = (TransactionId) currentCommandId;
+	Assert(maxsize >= c * sizeof(TransactionId));
 
 	/*
 	 * If we're running in a parallel worker and launching a parallel worker
@@ -4836,9 +4839,9 @@ SerializeTransactionState(Size maxsize, char *start_address)
 	 */
 	if (nParallelCurrentXids > 0)
 	{
-		Assert(maxsize > (nParallelCurrentXids + 4) * sizeof(TransactionId));
-		result[4] = nParallelCurrentXids;
-		memcpy(&result[5], ParallelCurrentXids,
+		result[c++] = nParallelCurrentXids;
+		Assert(maxsize >= (nParallelCurrentXids + c) * sizeof(TransactionId));
+		memcpy(&result[c], ParallelCurrentXids,
 			   nParallelCurrentXids * sizeof(TransactionId));
 		return;
 	}
@@ -4853,7 +4856,7 @@ SerializeTransactionState(Size maxsize, char *start_address)
 			nxids = add_size(nxids, 1);
 		nxids = add_size(nxids, s->nChildXids);
 	}
-	Assert(nxids * sizeof(TransactionId) < maxsize);
+	Assert((c + 1 + nxids) * sizeof(TransactionId) <= maxsize);
 
 	/* Copy them to our scratch space. */
 	workspace = palloc(nxids * sizeof(TransactionId));
@@ -4871,8 +4874,8 @@ SerializeTransactionState(Size maxsize, char *start_address)
 	qsort(workspace, nxids, sizeof(TransactionId), xidComparator);
 
 	/* Copy data into output area. */
-	result[4] = (TransactionId) nxids;
-	memcpy(&result[5], workspace, nxids * sizeof(TransactionId));
+	result[c++] = (TransactionId) nxids;
+	memcpy(&result[c], workspace, nxids * sizeof(TransactionId));
 }
 
 /*
@@ -4892,8 +4895,9 @@ StartParallelWorkerTransaction(char *tstatespace)
 	XactDeferrable = (bool) tstate[1];
 	XactTopTransactionId = tstate[2];
 	CurrentTransactionState->transactionId = tstate[3];
-	nParallelCurrentXids = (int) tstate[4];
-	ParallelCurrentXids = &tstate[5];
+	currentCommandId = tstate[4];
+	nParallelCurrentXids = (int) tstate[5];
+	ParallelCurrentXids = &tstate[6];
 
 	CurrentTransactionState->blockState = TBLOCK_PARALLEL_INPROGRESS;
 }