diff --git a/include/CppInterOp/CppInterOpRuntime.h b/include/CppInterOp/CppInterOpRuntime.h
new file mode 100644
index 000000000..22358fe44
--- /dev/null
+++ b/include/CppInterOp/CppInterOpRuntime.h
@@ -0,0 +1,22 @@
+//===--- CppInterOpRuntime.h - Runtime codes for language interoperability ---*- C++ -*-===//
+//
+// Part of the compiler-research project, under the Apache License v2.0 with
+// LLVM Exceptions.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef CPPINTEROP_CPPINTEROPRUNTIME_H
+#define CPPINTEROP_CPPINTEROPRUNTIME_H
+
+namespace __internal_CppInterOp {
+template <typename Signature>
+struct function;
+
+template <typename Res, typename... ArgTypes>
+struct function<Res(ArgTypes...)> {
+  using result_type = Res;
+};
+}  // namespace __internal_CppInterOp
+
+#endif // CPPINTEROP_CPPINTEROPRUNTIME_H
\ No newline at end of file
diff --git a/lib/CppInterOp/CppInterOp.cpp b/lib/CppInterOp/CppInterOp.cpp
index dd76109df..22d4b188a 100644
--- a/lib/CppInterOp/CppInterOp.cpp
+++ b/lib/CppInterOp/CppInterOp.cpp
@@ -3413,16 +3413,7 @@ TInterp_t CreateInterpreter(const std::vector<const char*>& Args /*={}*/,
 
   if (GetLanguage(I) != InterpreterLanguage::C) {
     I->declare(R"(
-    namespace __internal_CppInterOp {
-    template <typename Signature>
-    struct function;
-    template <typename Res, typename... ArgTypes>
-    struct function<Res(ArgTypes...)> {
-      typedef Res result_type;
-    };
-    }  // namespace __internal_CppInterOp
-  )");
-  }
+    #include <CppInterOp/CppInterOpRuntime.h>
 
   sInterpreters->emplace_back(I, /*Owned=*/true);