--- a/js/src/jit/IonBuilder.cpp
+++ b/js/src/jit/IonBuilder.cpp
@@ -12443,18 +12443,24 @@ IonBuilder::jsop_functionthis()
     // Hard case: |this| may be a primitive we have to wrap.
     MDefinition* def = current->getSlot(info().thisSlot());
 
     if (def->type() == MIRType::Object) {
         current->push(def);
         return Ok();
     }
 
+    // Beyond this point we may need to access non-syntactic global. Ion doesn't
+    // currently support this so just abort.
+    if (script()->hasNonSyntacticScope())
+        return abort(AbortReason::Disable, "JSOP_FUNCTIONTHIS would need non-syntactic global");
+
     if (IsNullOrUndefined(def->type())) {
-        pushConstant(GetThisValue(&script()->global()));
+        LexicalEnvironmentObject* globalLexical = &script()->global().lexicalEnvironment();
+        pushConstant(globalLexical->thisValue());
         return Ok();
     }
 
     MComputeThis* thisObj = MComputeThis::New(alloc(), def);
     current->add(thisObj);
     current->push(thisObj);
 
     return resumeAfter(thisObj);