diff --git a/eth/api.go b/eth/api.go
index 76118e2d7f..fd35656476 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 {