diff --git a/docs/developer_guides/appendix_b_api_reference.md b/docs/developer_guides/appendix_b_api_reference.md
index 3b6b380fdf..d82b682810 100644
--- a/docs/developer_guides/appendix_b_api_reference.md
+++ b/docs/developer_guides/appendix_b_api_reference.md
@@ -928,7 +928,7 @@ rpc DropIndex(DropIndexRequest) returns (common.Status){}
 
 **Description:**
 
-Drop a index for a collection.
+Drop an index for a collection.
 
 **Parameters:**