diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 2f1d4af17a..02b157243e 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -793,8 +793,13 @@ ProcArrayApplyRecoveryInfo(RunningTransactions running)
 		/*
 		 * Sort the array so that we can add them safely into
 		 * KnownAssignedXids.
+		 *
+		 * We have to sort them logically, because in KnownAssignedXidsAdd we
+		 * call TransactionIdFollowsOrEquals and so on. But we know these XIDs
+		 * come from RUNNING_XACTS, which means there are only normal XIDs from
+		 * the same epoch, so this is safe.
 		 */
-		qsort(xids, nxids, sizeof(TransactionId), xidComparator);
+		qsort(xids, nxids, sizeof(TransactionId), xidLogicalComparator);
 
 		/*
 		 * Add the sorted snapshot into KnownAssignedXids.  The running-xacts
diff --git a/src/backend/utils/adt/xid.c b/src/backend/utils/adt/xid.c
index 20389aff1d..5a083cecd4 100644
--- a/src/backend/utils/adt/xid.c
+++ b/src/backend/utils/adt/xid.c
@@ -148,6 +148,32 @@ xidComparator(const void *arg1, const void *arg2)
 	return 0;
 }
 
+/*
+ * xidLogicalComparator
+ *		qsort comparison function for XIDs
+ *
+ * This is used to compare only XIDs from the same epoch (e.g. for backends
+ * running at the same time). So there must be only normal XIDs, so there's
+ * no issue with triangle inequality.
+ */
+int
+xidLogicalComparator(const void *arg1, const void *arg2)
+{
+	TransactionId xid1 = *(const TransactionId *) arg1;
+	TransactionId xid2 = *(const TransactionId *) arg2;
+
+	Assert(TransactionIdIsNormal(xid1));
+	Assert(TransactionIdIsNormal(xid2));
+
+	if (TransactionIdPrecedes(xid1, xid2))
+		return -1;
+
+	if (TransactionIdPrecedes(xid2, xid1))
+		return 1;
+
+	return 0;
+}
+
 Datum
 xid8toxid(PG_FUNCTION_ARGS)
 {
diff --git a/src/include/utils/builtins.h b/src/include/utils/builtins.h
index a5c8772e95..c6ad51d522 100644
--- a/src/include/utils/builtins.h
+++ b/src/include/utils/builtins.h
@@ -89,6 +89,7 @@ extern void text_to_cstring_buffer(const text *src, char *dst, size_t dst_len);
 
 /* xid.c */
 extern int	xidComparator(const void *arg1, const void *arg2);
+extern int	xidLogicalComparator(const void *arg1, const void *arg2);
 
 /* inet_cidr_ntop.c */
 extern char *pg_inet_cidr_ntop(int af, const void *src, int bits,