diff --git a/update_metadata.proto b/update_metadata.proto
index f86cd8d..1120bd1 100644
--- a/update_metadata.proto
+++ b/update_metadata.proto
@@ -166,7 +166,7 @@
     REPLACE_XZ = 8; // Replace destination extents w/ attached xz data.
 
     // On minor version 4 or newer, these operations are supported:
-    IMGDIFF = 9; // The data is in imgdiff format.
+    PUFFDIFF = 9;  // The data is in puffdiff format.
   }
   required Type type = 1;
   // The offset into the delta file (after the protobuf)