diff --git a/core/chain_makers.go b/core/chain_makers.go
index 4f6fa3989..5a8f380a3 100644
--- a/core/chain_makers.go
+++ b/core/chain_makers.go
@@ -104,6 +104,11 @@ func (b *BlockGen) AddTx(tx *types.Transaction) {
 	b.receipts = append(b.receipts, receipt)
 }
 
+// Number returns the block number of the block being generated.
+func (b *BlockGen) Number() *big.Int {
+	return new(big.Int).Set(b.header.Number)
+}
+
 // AddUncheckedReceipts forcefully adds a receipts to the block without a
 // backing transaction.
 //
diff --git a/eth/downloader/downloader_test.go b/eth/downloader/downloader_test.go
index cfcc8a2ef..f02418a2f 100644
--- a/eth/downloader/downloader_test.go
+++ b/eth/downloader/downloader_test.go
@@ -61,8 +61,11 @@ func makeChain(n int, seed byte, parent *types.Block, parentReceipts types.Recei
 			block.AddTx(tx)
 		}
 		// If the block number is a multiple of 5, add a bonus uncle to the block
-		if i%5 == 0 {
-			block.AddUncle(&types.Header{ParentHash: block.PrevBlock(i - 1).Hash(), Number: big.NewInt(int64(i - 1))})
+		if i > 0 && i%5 == 0 {
+			block.AddUncle(&types.Header{
+				ParentHash: block.PrevBlock(i - 1).Hash(),
+				Number:     big.NewInt(block.Number().Int64() - 1),
+			})
 		}
 	})
 	// Convert the block-chain into a hash-chain and header/block maps