diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index bf2f4dbed2..908f62d37e 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -799,10 +799,21 @@ ProcArrayApplyRecoveryInfo(RunningTransactions running)
 		qsort(xids, nxids, sizeof(TransactionId), xidComparator);
 
 		/*
-		 * Add the sorted snapshot into KnownAssignedXids
+		 * Add the sorted snapshot into KnownAssignedXids.  The running-xacts
+		 * snapshot may include duplicated xids because of prepared
+		 * transactions, so ignore them.
 		 */
 		for (i = 0; i < nxids; i++)
+		{
+			if (i > 0 && TransactionIdEquals(xids[i - 1], xids[i]))
+			{
+				elog(DEBUG1,
+					 "found duplicated transaction %u for KnownAssignedXids insertion",
+					 xids[i]);
+				continue;
+			}
 			KnownAssignedXidsAdd(xids[i], xids[i], true);
+		}
 
 		KnownAssignedXidsDisplay(trace_recovery(DEBUG3));
 	}
@@ -1898,7 +1909,8 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
  * GetRunningTransactionData -- returns information about running transactions.
  *
  * Similar to GetSnapshotData but returns more information. We include
- * all PGXACTs with an assigned TransactionId, even VACUUM processes.
+ * all PGXACTs with an assigned TransactionId, even VACUUM processes and
+ * prepared transactions.
  *
  * We acquire XidGenLock and ProcArrayLock, but the caller is responsible for
  * releasing them. Acquiring XidGenLock ensures that no new XIDs enter the proc
@@ -1912,6 +1924,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
  * This is never executed during recovery so there is no need to look at
  * KnownAssignedXids.
  *
+ * Dummy PGXACTs from prepared transaction are included, meaning that this
+ * may return entries with duplicated TransactionId values coming from
+ * transaction finishing to prepare.  Nothing is done about duplicated
+ * entries here to not hold on ProcArrayLock more than necessary.
+ *
  * We don't worry about updating other counters, we want to keep this as
  * simple as possible and leave GetSnapshotData() as the primary code for
  * that bookkeeping.