diff --git a/CMakeLists.txt b/CMakeLists.txt
index 159ffee..4e033eb 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -114,5 +114,5 @@ target_link_libraries(mcc
 
 ## 6. Build the runtime library too
 
-add_library(mcrt STATIC Runtime.cpp)
+add_library(mcrt STATIC Runtime.c)
 
diff --git a/Runtime.cpp b/Runtime.c
similarity index 96%
rename from Runtime.cpp
rename to Runtime.c
index 9885a8e..cfa6c2e 100644
--- a/Runtime.cpp
+++ b/Runtime.c
@@ -17,11 +17,11 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-#include "Runtime.hpp"
+#include "Runtime.h"
 
-#include <cstdio>
-#include <cstdlib>
-#include <cassert>
+#include <stdio.h>
+#include <stdlib.h>
+#include <assert.h>
 
 
 void Monicelli_putBool(Monicelli_Bool value) {
diff --git a/Runtime.hpp b/Runtime.h
similarity index 100%
rename from Runtime.hpp
rename to Runtime.h