--- a/js/src/ion/TypePolicy.cpp
+++ b/js/src/ion/TypePolicy.cpp
@@ -155,36 +155,37 @@ ComparePolicy::adjustInputs(MInstruction
             def->replaceOperand(1, unbox);
         }
 
         JS_ASSERT(def->getOperand(0)->type() != MIRType_String);
         JS_ASSERT(def->getOperand(1)->type() == MIRType_String);
         return true;
     }
 
+    if (compare->compareType() == MCompare::Compare_Undefined ||
+        compare->compareType() == MCompare::Compare_Null)
+    {
+        // Nothing to do for undefined and null, lowering handles all types.
+        return true;
+    }
+
     // Convert all inputs to the right input type
     MIRType type = compare->inputType();
-
-    // Nothing to do for undefined and null, lowering handles all types.
-    if (type == MIRType_Undefined || type == MIRType_Null)
-        return true;
-
+    JS_ASSERT(type == MIRType_Int32 || type == MIRType_Double ||
+              type == MIRType_Object || type == MIRType_String);
     for (size_t i = 0; i < 2; i++) {
         MDefinition *in = def->getOperand(i);
         if (in->type() == type)
             continue;
 
         MInstruction *replace;
 
         // See BinaryArithPolicy::adjustInputs for an explanation of the following
-        if (in->type() == MIRType_Object || in->type() == MIRType_String ||
-            (in->type() == MIRType_Boolean && type != MIRType_Double && type != MIRType_Int32))
-        {
+        if (in->type() == MIRType_Object || in->type() == MIRType_String)
             in = boxAt(def, in);
-        }
 
         switch (type) {
           case MIRType_Double:
             replace = MToDouble::New(in);
             break;
           case MIRType_Int32:
             replace = MToInt32::New(in);
             break;

new file mode 100644
--- /dev/null
+++ b/js/src/jit-test/tests/ion/bug852140.js
@@ -0,0 +1,7 @@
+function reportCompare (expected, actual) {
+  if (expected != actual) {}
+}
+function exitFunc (funcName)
+  reportCompare(undefined, '');
+reportCompare('', '');
+exitFunc();