diff --git a/src/backend/utils/time/combocid.c b/src/backend/utils/time/combocid.c
index 85de85adf86d382fbb6b98e50588817011b0f5b9..12bc2eedfeb12b8e56a57aa66118b3e4205e4909 100644
--- a/src/backend/utils/time/combocid.c
+++ b/src/backend/utils/time/combocid.c
@@ -208,6 +208,13 @@ GetComboCommandId(CommandId cmin, CommandId cmax)
 	{
 		HASHCTL		hash_ctl;
 
+		/* Make array first; existence of hash table asserts array exists */
+		comboCids = (ComboCidKeyData *)
+			MemoryContextAlloc(TopTransactionContext,
+							   sizeof(ComboCidKeyData) * CCID_ARRAY_SIZE);
+		sizeComboCids = CCID_ARRAY_SIZE;
+		usedComboCids = 0;
+
 		memset(&hash_ctl, 0, sizeof(hash_ctl));
 		hash_ctl.keysize = sizeof(ComboCidKeyData);
 		hash_ctl.entrysize = sizeof(ComboCidEntryData);
@@ -218,12 +225,20 @@ GetComboCommandId(CommandId cmin, CommandId cmax)
 								CCID_HASH_SIZE,
 								&hash_ctl,
 								HASH_ELEM | HASH_FUNCTION | HASH_CONTEXT);
+	}
+
+	/*
+	 * Grow the array if there's not at least one free slot.  We must do this
+	 * before possibly entering a new hashtable entry, else failure to
+	 * repalloc would leave a corrupt hashtable entry behind.
+	 */
+	if (usedComboCids >= sizeComboCids)
+	{
+		int			newsize = sizeComboCids * 2;
 
 		comboCids = (ComboCidKeyData *)
-			MemoryContextAlloc(TopTransactionContext,
-							   sizeof(ComboCidKeyData) * CCID_ARRAY_SIZE);
-		sizeComboCids = CCID_ARRAY_SIZE;
-		usedComboCids = 0;
+			repalloc(comboCids, sizeof(ComboCidKeyData) * newsize);
+		sizeComboCids = newsize;
 	}
 
 	/* Lookup or create a hash entry with the desired cmin/cmax */
@@ -242,20 +257,7 @@ GetComboCommandId(CommandId cmin, CommandId cmax)
 		return entry->combocid;
 	}
 
-	/*
-	 * We have to create a new combo cid. Check that there's room for it in
-	 * the array, and grow it if there isn't.
-	 */
-	if (usedComboCids >= sizeComboCids)
-	{
-		/* We need to grow the array */
-		int			newsize = sizeComboCids * 2;
-
-		comboCids = (ComboCidKeyData *)
-			repalloc(comboCids, sizeof(ComboCidKeyData) * newsize);
-		sizeComboCids = newsize;
-	}
-
+	/* We have to create a new combo cid; we already made room in the array */
 	combocid = usedComboCids;
 
 	comboCids[combocid].cmin = cmin;