diff --git a/eth/api.go b/eth/api.go
index 76118e2d7fc683555a995fad795d8dc3b5fde14d..fd3565647647b75da6dbc2575c803509129f7c1f 100644
--- a/eth/api.go
+++ b/eth/api.go
@@ -389,6 +389,8 @@ func (api *PublicDebugAPI) AccountRange(blockNrOrHash rpc.BlockNumberOrHash, sta
 		if err != nil {
 			return state.IteratorDump{}, err
 		}
+	} else {
+		return state.IteratorDump{}, errors.New("either block number or block hash must be specified")
 	}
 
 	if maxResults > AccountRangeMaxResults || maxResults <= 0 {