--- a/js/src/jit/MIR.h
+++ b/js/src/jit/MIR.h
@@ -2633,16 +2633,19 @@ class MCreateThisWithProto
     MDefinition *getPrototype() const {
         return getOperand(1);
     }
 
     // Although creation of |this| modifies global state, it is safely repeatable.
     AliasSet getAliasSet() const {
         return AliasSet::None();
     }
+    bool congruentTo(MDefinition *ins) const {
+        return false;
+    }
     TypePolicy *typePolicy() {
         return this;
     }
     bool possiblyCalls() const {
         return true;
     }
 };
 
@@ -4400,16 +4403,19 @@ class MStringSplit
         return getOperand(1);
     }
     TypePolicy *typePolicy() {
         return this;
     }
     bool possiblyCalls() const {
         return true;
     }
+    bool congruentTo(MDefinition *ins) const {
+        return false;
+    }
     virtual AliasSet getAliasSet() const {
         // Although this instruction returns a new array, we don't have to mark
         // it as store instruction, see also MNewArray.
         return AliasSet::None();
     }
 };
 
 // Returns an object to use as |this| value. See also ComputeThis and