diff --git a/test/cctest/test-api.cc b/test/cctest/test-api.cc
index d7ba7d7c7d..6bf092dafe 100644
--- a/test/cctest/test-api.cc
+++ b/test/cctest/test-api.cc
@@ -331,16 +331,14 @@ static uint16_t* AsciiToTwoByteString(const char* source) {
 
 class TestResource: public String::ExternalStringResource {
  public:
-  static int dispose_count;
-
-  explicit TestResource(uint16_t* data)
-      : data_(data), length_(0) {
+  explicit TestResource(uint16_t* data, int* counter = NULL)
+    : data_(data), length_(0), counter_(counter) {
     while (data[length_]) ++length_;
   }
 
   ~TestResource() {
     i::DeleteArray(data_);
-    ++dispose_count;
+    if (counter_ != NULL) ++*counter_;
   }
 
   const uint16_t* data() const {
@@ -353,23 +351,18 @@ class TestResource: public String::ExternalStringResource {
  private:
   uint16_t* data_;
   size_t length_;
+  int* counter_;
 };
 
 
-int TestResource::dispose_count = 0;
-
-
 class TestAsciiResource: public String::ExternalAsciiStringResource {
  public:
-  static int dispose_count;
-
-  explicit TestAsciiResource(const char* data)
-      : data_(data),
-        length_(strlen(data)) { }
+  explicit TestAsciiResource(const char* data, int* counter = NULL)
+    : data_(data), length_(strlen(data)), counter_(counter) { }
 
   ~TestAsciiResource() {
     i::DeleteArray(data_);
-    ++dispose_count;
+    if (counter_ != NULL) ++*counter_;
   }
 
   const char* data() const {
@@ -382,20 +375,18 @@ class TestAsciiResource: public String::ExternalAsciiStringResource {
  private:
   const char* data_;
   size_t length_;
+  int* counter_;
 };
 
 
-int TestAsciiResource::dispose_count = 0;
-
-
 THREADED_TEST(ScriptUsingStringResource) {
-  TestResource::dispose_count = 0;
+  int dispose_count = 0;
   const char* c_source = "1 + 2 * 3";
   uint16_t* two_byte_source = AsciiToTwoByteString(c_source);
   {
     v8::HandleScope scope;
     LocalContext env;
-    TestResource* resource = new TestResource(two_byte_source);
+    TestResource* resource = new TestResource(two_byte_source, &dispose_count);
     Local<String> source = String::NewExternal(resource);
     Local<Script> script = Script::Compile(source);
     Local<Value> value = script->Run();
@@ -405,37 +396,38 @@ THREADED_TEST(ScriptUsingStringResource) {
     CHECK_EQ(resource,
              static_cast<TestResource*>(source->GetExternalStringResource()));
     HEAP->CollectAllGarbage(false);
-    CHECK_EQ(0, TestResource::dispose_count);
+    CHECK_EQ(0, dispose_count);
   }
   v8::internal::Isolate::Current()->compilation_cache()->Clear();
   HEAP->CollectAllGarbage(false);
-  CHECK_EQ(1, TestResource::dispose_count);
+  CHECK_EQ(1, dispose_count);
 }
 
 
 THREADED_TEST(ScriptUsingAsciiStringResource) {
-  TestAsciiResource::dispose_count = 0;
+  int dispose_count = 0;
   const char* c_source = "1 + 2 * 3";
   {
     v8::HandleScope scope;
     LocalContext env;
     Local<String> source =
-        String::NewExternal(new TestAsciiResource(i::StrDup(c_source)));
+        String::NewExternal(new TestAsciiResource(i::StrDup(c_source),
+                                                  &dispose_count));
     Local<Script> script = Script::Compile(source);
     Local<Value> value = script->Run();
     CHECK(value->IsNumber());
     CHECK_EQ(7, value->Int32Value());
     HEAP->CollectAllGarbage(false);
-    CHECK_EQ(0, TestAsciiResource::dispose_count);
+    CHECK_EQ(0, dispose_count);
   }
   i::Isolate::Current()->compilation_cache()->Clear();
   HEAP->CollectAllGarbage(false);
-  CHECK_EQ(1, TestAsciiResource::dispose_count);
+  CHECK_EQ(1, dispose_count);
 }
 
 
 THREADED_TEST(ScriptMakingExternalString) {
-  TestResource::dispose_count = 0;
+  int dispose_count = 0;
   uint16_t* two_byte_source = AsciiToTwoByteString("1 + 2 * 3");
   {
     v8::HandleScope scope;
@@ -444,23 +436,24 @@ THREADED_TEST(ScriptMakingExternalString) {
     // Trigger GCs so that the newly allocated string moves to old gen.
     HEAP->CollectGarbage(i::NEW_SPACE);  // in survivor space now
     HEAP->CollectGarbage(i::NEW_SPACE);  // in old gen now
-    bool success = source->MakeExternal(new TestResource(two_byte_source));
+    bool success = source->MakeExternal(new TestResource(two_byte_source,
+                                                         &dispose_count));
     CHECK(success);
     Local<Script> script = Script::Compile(source);
     Local<Value> value = script->Run();
     CHECK(value->IsNumber());
     CHECK_EQ(7, value->Int32Value());
     HEAP->CollectAllGarbage(false);
-    CHECK_EQ(0, TestResource::dispose_count);
+    CHECK_EQ(0, dispose_count);
   }
   i::Isolate::Current()->compilation_cache()->Clear();
   HEAP->CollectAllGarbage(false);
-  CHECK_EQ(1, TestResource::dispose_count);
+  CHECK_EQ(1, dispose_count);
 }
 
 
 THREADED_TEST(ScriptMakingExternalAsciiString) {
-  TestAsciiResource::dispose_count = 0;
+  int dispose_count = 0;
   const char* c_source = "1 + 2 * 3";
   {
     v8::HandleScope scope;
@@ -470,18 +463,18 @@ THREADED_TEST(ScriptMakingExternalAsciiString) {
     HEAP->CollectGarbage(i::NEW_SPACE);  // in survivor space now
     HEAP->CollectGarbage(i::NEW_SPACE);  // in old gen now
     bool success = source->MakeExternal(
-        new TestAsciiResource(i::StrDup(c_source)));
+        new TestAsciiResource(i::StrDup(c_source), &dispose_count));
     CHECK(success);
     Local<Script> script = Script::Compile(source);
     Local<Value> value = script->Run();
     CHECK(value->IsNumber());
     CHECK_EQ(7, value->Int32Value());
     HEAP->CollectAllGarbage(false);
-    CHECK_EQ(0, TestAsciiResource::dispose_count);
+    CHECK_EQ(0, dispose_count);
   }
   i::Isolate::Current()->compilation_cache()->Clear();
   HEAP->CollectAllGarbage(false);
-  CHECK_EQ(1, TestAsciiResource::dispose_count);
+  CHECK_EQ(1, dispose_count);
 }
 
 
@@ -605,49 +598,52 @@ THREADED_TEST(UsingExternalAsciiString) {
 
 
 THREADED_TEST(ScavengeExternalString) {
-  TestResource::dispose_count = 0;
+  int dispose_count = 0;
   bool in_new_space = false;
   {
     v8::HandleScope scope;
     uint16_t* two_byte_string = AsciiToTwoByteString("test string");
     Local<String> string =
-        String::NewExternal(new TestResource(two_byte_string));
+      String::NewExternal(new TestResource(two_byte_string,
+                                           &dispose_count));
     i::Handle<i::String> istring = v8::Utils::OpenHandle(*string);
     HEAP->CollectGarbage(i::NEW_SPACE);
     in_new_space = HEAP->InNewSpace(*istring);
     CHECK(in_new_space || HEAP->old_data_space()->Contains(*istring));
-    CHECK_EQ(0, TestResource::dispose_count);
+    CHECK_EQ(0, dispose_count);
   }
   HEAP->CollectGarbage(in_new_space ? i::NEW_SPACE : i::OLD_DATA_SPACE);
-  CHECK_EQ(1, TestResource::dispose_count);
+  CHECK_EQ(1, dispose_count);
 }
 
 
 THREADED_TEST(ScavengeExternalAsciiString) {
-  TestAsciiResource::dispose_count = 0;
+  int dispose_count = 0;
   bool in_new_space = false;
   {
     v8::HandleScope scope;
     const char* one_byte_string = "test string";
     Local<String> string = String::NewExternal(
-        new TestAsciiResource(i::StrDup(one_byte_string)));
+        new TestAsciiResource(i::StrDup(one_byte_string), &dispose_count));
     i::Handle<i::String> istring = v8::Utils::OpenHandle(*string);
     HEAP->CollectGarbage(i::NEW_SPACE);
     in_new_space = HEAP->InNewSpace(*istring);
     CHECK(in_new_space || HEAP->old_data_space()->Contains(*istring));
-    CHECK_EQ(0, TestAsciiResource::dispose_count);
+    CHECK_EQ(0, dispose_count);
   }
   HEAP->CollectGarbage(in_new_space ? i::NEW_SPACE : i::OLD_DATA_SPACE);
-  CHECK_EQ(1, TestAsciiResource::dispose_count);
+  CHECK_EQ(1, dispose_count);
 }
 
 
 class TestAsciiResourceWithDisposeControl: public TestAsciiResource {
  public:
+  // Only used by non-threaded tests, so it can use static fields.
   static int dispose_calls;
+  static int dispose_count;
 
   TestAsciiResourceWithDisposeControl(const char* data, bool dispose)
-      : TestAsciiResource(data),
+      : TestAsciiResource(data, &dispose_count),
         dispose_(dispose) { }
 
   void Dispose() {
@@ -659,6 +655,7 @@ class TestAsciiResourceWithDisposeControl: public TestAsciiResource {
 };
 
 
+int TestAsciiResourceWithDisposeControl::dispose_count = 0;
 int TestAsciiResourceWithDisposeControl::dispose_calls = 0;
 
 
@@ -666,7 +663,7 @@ TEST(ExternalStringWithDisposeHandling) {
   const char* c_source = "1 + 2 * 3";
 
   // Use a stack allocated external string resource allocated object.
-  TestAsciiResource::dispose_count = 0;
+  TestAsciiResourceWithDisposeControl::dispose_count = 0;
   TestAsciiResourceWithDisposeControl::dispose_calls = 0;
   TestAsciiResourceWithDisposeControl res_stack(i::StrDup(c_source), false);
   {
@@ -678,15 +675,15 @@ TEST(ExternalStringWithDisposeHandling) {
     CHECK(value->IsNumber());
     CHECK_EQ(7, value->Int32Value());
     HEAP->CollectAllGarbage(false);
-    CHECK_EQ(0, TestAsciiResource::dispose_count);
+    CHECK_EQ(0, TestAsciiResourceWithDisposeControl::dispose_count);
   }
   i::Isolate::Current()->compilation_cache()->Clear();
   HEAP->CollectAllGarbage(false);
   CHECK_EQ(1, TestAsciiResourceWithDisposeControl::dispose_calls);
-  CHECK_EQ(0, TestAsciiResource::dispose_count);
+  CHECK_EQ(0, TestAsciiResourceWithDisposeControl::dispose_count);
 
   // Use a heap allocated external string resource allocated object.
-  TestAsciiResource::dispose_count = 0;
+  TestAsciiResourceWithDisposeControl::dispose_count = 0;
   TestAsciiResourceWithDisposeControl::dispose_calls = 0;
   TestAsciiResource* res_heap =
       new TestAsciiResourceWithDisposeControl(i::StrDup(c_source), true);
@@ -699,12 +696,12 @@ TEST(ExternalStringWithDisposeHandling) {
     CHECK(value->IsNumber());
     CHECK_EQ(7, value->Int32Value());
     HEAP->CollectAllGarbage(false);
-    CHECK_EQ(0, TestAsciiResource::dispose_count);
+    CHECK_EQ(0, TestAsciiResourceWithDisposeControl::dispose_count);
   }
   i::Isolate::Current()->compilation_cache()->Clear();
   HEAP->CollectAllGarbage(false);
   CHECK_EQ(1, TestAsciiResourceWithDisposeControl::dispose_calls);
-  CHECK_EQ(1, TestAsciiResource::dispose_count);
+  CHECK_EQ(1, TestAsciiResourceWithDisposeControl::dispose_count);
 }