--- \dll\postgresql-12.0\a\backend\access\transam\xact.c	Mon Sep 30 17:06:55 2019
+++ xact.c	Wed Nov 13 13:03:28 2019
@@ -1580,20 +1580,20 @@
 	 */
 	s->parent->childXids[s->parent->nChildXids] = XidFromFullTransactionId(s->fullTransactionId);
 
-	if (s->nChildXids > 0)
+	if (s->childXids != NULL) {
 		memcpy(&s->parent->childXids[s->parent->nChildXids + 1],
 			   s->childXids,
 			   s->nChildXids * sizeof(TransactionId));
+	    /* Release child's array to avoid leakage */
+        pfree(s->childXids);
 
+	    /* We must reset these to avoid double-free if fail later in commit */
+	    s->childXids = NULL;
+	    s->nChildXids = 0;
+	    s->maxChildXids = 0;
+    }
+	Assert(s->nChildXids == 0 && s->maxChildXids == 0);
 	s->parent->nChildXids = new_nChildXids;
-
-	/* Release child's array to avoid leakage */
-	if (s->childXids != NULL)
-		pfree(s->childXids);
-	/* We must reset these to avoid double-free if fail later in commit */
-	s->childXids = NULL;
-	s->nChildXids = 0;
-	s->maxChildXids = 0;
 }
 
 /* ----------------------------------------------------------------