diff --git a/fxjs/gc/heap.cpp b/fxjs/gc/heap.cpp
index d75c675..9dade5c 100644
--- a/fxjs/gc/heap.cpp
+++ b/fxjs/gc/heap.cpp
@@ -4,6 +4,7 @@
 
 #include "fxjs/gc/heap.h"
 
+#include "core/fxcrt/fx_system.h"
 #include "third_party/base/ptr_util.h"
 
 namespace {
@@ -42,6 +43,7 @@
 
 void FXGC_Initialize(v8::Platform* platform) {
   if (platform) {
+    ASSERT(!g_platform);
     g_platform = platform;
     cppgc::InitializeProcess(platform->GetPageAllocator());
   }
@@ -68,9 +70,8 @@
 }
 
 void FXGCHeapDeleter::operator()(cppgc::Heap* heap) {
-  if (!heap)
-    return;
-
+  ASSERT(heap);
+  ASSERT(g_platform_ref_count > 0);
   --g_platform_ref_count;
   delete heap;
 }
diff --git a/fxjs/gc/heap_embeddertest.cpp b/fxjs/gc/heap_embeddertest.cpp
index 5f77914..4930d44 100644
--- a/fxjs/gc/heap_embeddertest.cpp
+++ b/fxjs/gc/heap_embeddertest.cpp
@@ -58,7 +58,13 @@
   EXPECT_TRUE(heap2);
 
   FXGCScopedHeap heap3 = FXGC_CreateHeap();
-  EXPECT_TRUE(heap2);
+  EXPECT_TRUE(heap3);
+
+  // Test manually destroying the heap.
+  heap3.reset();
+  EXPECT_FALSE(heap3);
+  heap3.reset();
+  EXPECT_FALSE(heap3);
 }
 
 TEST_F(HeapEmbedderTest, NoReferences) {