diff --git a/data/json/mutations/mutations.json b/data/json/mutations/mutations.json
index e639633bcd3a9..c158097b2ebf6 100644
--- a/data/json/mutations/mutations.json
+++ b/data/json/mutations/mutations.json
@@ -991,6 +991,7 @@
     "points": -1,
     "description": "Whether due to injury or age, your knees aren't particularly strong or flexible.  Moving over rough terrain will slow you down more than normal.",
     "starting_trait": true,
+    "cancels": [ "STRONGKNEES" ],
     "valid": false,
     "movecost_obstacle_modifier": 1.25
   },
@@ -1001,6 +1002,7 @@
     "points": 1,
     "description": "Your knees are strong and capable of angles that you couldn't imagine previously.  Moving over rough terrain will slow you down less than normal.",
     "category": [ "BATRACHIAN" ],
+    "cancels": [ "BADKNEES" ],
     "valid": false,
     "movecost_obstacle_modifier": 0.9
   },