diff --git a/js/src/builtin/TestingFunctions.cpp b/js/src/builtin/TestingFunctions.cpp
index 318eb53303d..1ac7b606aa2 100644
--- a/js/src/builtin/TestingFunctions.cpp
+++ b/js/src/builtin/TestingFunctions.cpp
@@ -1245,8 +1245,11 @@ ReadSPSProfilingStack(JSContext *cx, unsigned argc, jsval *vp)
     CallArgs args = CallArgsFromVp(argc, vp);
     args.rval().setUndefined();
 
-    if (!cx->runtime()->spsProfiler.enabled())
+    // Return boolean 'false' if profiler is not enabled.
+    if (!cx->runtime()->spsProfiler.enabled()) {
         args.rval().setBoolean(false);
+        return true;
+    }
 
     // Array holding physical jit stack frames.
     RootedObject stack(cx, NewDenseEmptyArray(cx));
diff --git a/js/src/vm/Stack.cpp b/js/src/vm/Stack.cpp
index 670c05fa93d..9565cde6428 100644
--- a/js/src/vm/Stack.cpp
+++ b/js/src/vm/Stack.cpp
@@ -1719,6 +1719,9 @@ JS::ProfilingFrameIterator::ProfilingFrameIterator(JSRuntime *rt, const Register
     activation_(rt->profilingActivation()),
     savedPrevJitTop_(nullptr)
 {
+    // Should only be instantiated when profiling is enabled.
+    MOZ_ASSERT(rt_->spsProfiler.enabled());
+
     if (!activation_)
         return;