diff --git a/js/src/vm/EnvironmentObject.cpp b/js/src/vm/EnvironmentObject.cpp
index 1c87e552ca..5ea7971e0e 100644
--- a/js/src/vm/EnvironmentObject.cpp
+++ b/js/src/vm/EnvironmentObject.cpp
@@ -633,7 +633,7 @@ const Class WasmFunctionCallObject::class_ = {
 };
 
 /* static */ WasmFunctionCallObject*
-WasmFunctionCallObject::createHollowForDebug(JSContext* cx, WasmFunctionScope* scope)
+WasmFunctionCallObject::createHollowForDebug(JSContext* cx, Handle<WasmFunctionScope*> scope)
 {
     RootedObjectGroup group(cx, ObjectGroup::defaultNewGroup(cx, &class_, TaggedProto(nullptr)));
     if (!group)
@@ -652,6 +652,7 @@ WasmFunctionCallObject::createHollowForDebug(JSContext* cx, WasmFunctionScope* s
 
     Rooted<WasmFunctionCallObject*> callobj(cx, &obj->as<WasmFunctionCallObject>());
     callobj->initEnclosingEnvironment(&cx->global()->lexicalEnvironment());
+    callobj->initReservedSlot(SCOPE_SLOT, PrivateGCThingValue(scope));
 
     return callobj;
 }
diff --git a/js/src/vm/EnvironmentObject.h b/js/src/vm/EnvironmentObject.h
index 63eded443b..4c7e53adcc 100644
--- a/js/src/vm/EnvironmentObject.h
+++ b/js/src/vm/EnvironmentObject.h
@@ -427,13 +427,19 @@ typedef MutableHandle<ModuleEnvironmentObject*> MutableHandleModuleEnvironmentOb
 
 class WasmFunctionCallObject : public EnvironmentObject
 {
+  // Currently WasmFunctionCallObjects do not use their scopes in a
+    // meaningful way. However, it is an invariant of DebugEnvironments that
+    // environments kept in those maps have live scopes, thus this strong
+    // reference.
+    static const uint32_t SCOPE_SLOT = 1;
+
   public:
     static const Class class_;
 
-    static const uint32_t RESERVED_SLOTS = 1;
+    static const uint32_t RESERVED_SLOTS = 2;
 
     static WasmFunctionCallObject* createHollowForDebug(JSContext* cx,
-                                                        WasmFunctionScope* scope);
+                                                        Handle<WasmFunctionScope*> scope);
 };
 
 class LexicalEnvironmentObject : public EnvironmentObject