diff --git a/lib/CppInterOp/CppInterOp.cpp b/lib/CppInterOp/CppInterOp.cpp
index 46f2fe226..0aba093cc 100755
--- a/lib/CppInterOp/CppInterOp.cpp
+++ b/lib/CppInterOp/CppInterOp.cpp
@@ -9,6 +9,8 @@
 
 #include "CppInterOp/CppInterOp.h"
 
+#include "CppInterOpRuntime.h"
+
 #include "Compatibility.h"
 
 #include "clang/AST/Attrs.inc"
@@ -3268,14 +3270,7 @@ TInterp_t CreateInterpreter(const std::vector<const char*>& Args /*={}*/,
   }
 
   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 "CppInterOpRuntime.h"
   )");
 
   sInterpreters->emplace_back(I, /*Owned=*/true);
diff --git a/lib/CppInterOp/CppInterOpRuntime.h b/lib/CppInterOp/CppInterOpRuntime.h
new file mode 100644
index 000000000..2e5b7fbe8
--- /dev/null
+++ b/lib/CppInterOp/CppInterOpRuntime.h
@@ -0,0 +1,19 @@
+#ifndef CPPINTEROP_RUNTIME_H
+#define CPPINTEROP_RUNTIME_H
+
+// This header contains runtime utilities previously injected into the
+// interpreter using I->declare(). It is now provided as a real header so that
+// the interpreter can load it on startup.
+
+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_RUNTIME_H