diff --git a/collection/opendb-city-china/collection.json b/collection/opendb-city-china/collection.json
index eb736a8..00fc190 100644
--- a/collection/opendb-city-china/collection.json
+++ b/collection/opendb-city-china/collection.json
@@ -67,10 +67,10 @@
       }
     },
     {
-      "IndexName": "letter",
+      "IndexName": "first_letter",
       "MgoKeySchema": {
         "MgoIndexKeys": [{
-          "Name": "letter",
+          "Name": "first_letter",
           "Direction": "1"
         }],
         "MgoIsUnique": false
diff --git a/collection/opendb-nation-china/collection.json b/collection/opendb-nation-china/collection.json
index 9376bbc..d554f1f 100644
--- a/collection/opendb-nation-china/collection.json
+++ b/collection/opendb-nation-china/collection.json
@@ -47,10 +47,10 @@
       }
     },
     {
-      "IndexName": "letter",
+      "IndexName": "first_letter",
       "MgoKeySchema": {
         "MgoIndexKeys": [{
-          "Name": "letter",
+          "Name": "first_letter",
           "Direction": "1"
         }],
         "MgoIsUnique": false