diff --git a/extras/test.cpp b/extras/test.cpp
index 1394590..f680df7 100644
--- a/extras/test.cpp
+++ b/extras/test.cpp
@@ -8,6 +8,7 @@
 *******************************************************************************/
 
 #include <list>
+#include <string>
 #include <vector>
 
 namespace stdcpp {
@@ -16,9 +17,17 @@ namespace stdcpp {
         std::size_t cppSizeOf() {
             return sizeof(T);
         }
+
+        /// Returns the result of `std::string` capacity with the provided string
+        std::size_t stringCapacity (char const* str) {
+            std::string s(str);
+            return s.capacity();
+        }
     };
 };
 
+template std::size_t stdcpp::test::cppSizeOf<std::string>();
+
 template class std::list<int>;
 template std::size_t stdcpp::test::cppSizeOf<std::list<int> >();
 
diff --git a/source/stdcpp/test/string.d b/source/stdcpp/test/string.d
index f10ec04..13c8a9c 100644
--- a/source/stdcpp/test/string.d
+++ b/source/stdcpp/test/string.d
@@ -5,16 +5,23 @@
 *******************************************************************************/
 
 module stdcpp.test.string;
+
+import stdcpp.test.base;
 import stdcpp.string;
-version (CppRuntime_Gcc)
+
+extern(C++, "stdcpp", "test") size_t stringCapacity (const(char)* str);
+
+/// Test that the sizes matches
+unittest
+{
+    assert(cppSizeOf!(std_string) == std_string.sizeof);
+}
+
+unittest
 {
-    unittest
-    {
-        auto a = std_string("hello");
-        a.push_back('a');
-        assert(a.size() == 6);
-        assert(std_string.sizeof == 32);
-        // verifying small string optimization
-        assert(a.capacity == 15);
-    }
-}
\ No newline at end of file
+    auto a = std_string("hello");
+    a.push_back('a');
+    assert(a.size() == 6);
+    // verifying small string optimization, this is 15 on GCC, 22-23 on clang
+    assert(a.capacity == stringCapacity("hello"));
+}