diff --git a/paddle/fluid/framework/framework.proto b/paddle/fluid/framework/framework.proto
index 8c57ae3e993bd7c2369996070e920acaf9c506d7..22d06923948e17cc8cd9278a4dba53acefcce4db 100644
--- a/paddle/fluid/framework/framework.proto
+++ b/paddle/fluid/framework/framework.proto
@@ -117,6 +117,7 @@ message VarType {
   required Type type = 1;
 
   message TensorDesc {
+    // Should only be PODType. Is enforced in C++
     required Type data_type = 1;
     repeated int64 dims = 2; // [UNK, 640, 480] is saved as [-1, 640, 480]
   }