diff --git a/eth/api_backend.go b/eth/api_backend.go
index 57f5a50837..8ec19308f9 100644
--- a/eth/api_backend.go
+++ b/eth/api_backend.go
@@ -196,7 +196,9 @@ func (b *EthAPIBackend) BlockByNumberOrHash(ctx context.Context, blockNrOrHash r
 	if hash, ok := blockNrOrHash.Hash(); ok {
 		header := b.eth.blockchain.GetHeaderByHash(hash)
 		if header == nil {
-			return nil, errors.New("header for hash not found")
+			// Return 'null' and no error if block is not found.
+			// This behavior is required by RPC spec.
+			return nil, nil
 		}
 		if blockNrOrHash.RequireCanonical && b.eth.blockchain.GetCanonicalHash(header.Number.Uint64()) != hash {
 			return nil, errors.New("hash is not currently canonical")