diff --git a/eth/downloader/testchain_test.go b/eth/downloader/testchain_test.go
index 8fa2e83413..1bf895c0ee 100644
--- a/eth/downloader/testchain_test.go
+++ b/eth/downloader/testchain_test.go
@@ -210,7 +210,7 @@ func newTestBlockchain(blocks []*types.Block) *core.BlockChain {
 		testBlockchains[head] = new(testBlockchain)
 	}
 	tbc := testBlockchains[head]
-	testBlockchainsLock.Unlock()
+	defer testBlockchainsLock.Unlock()
 
 	// Ensure that the database is generated
 	tbc.gen.Do(func() {