diff --git a/mmap/mmap_unmap.c b/mmap/mmap_unmap.c
new file mode 100644
index 0000000..cc638ed
--- /dev/null
+++ b/mmap/mmap_unmap.c
@@ -0,0 +1,18 @@
+#include <sys/types.h>
+#include <unistd.h>
+#ifdef __MINGW32__
+#include <windows.h>
+#else
+#include <sys/mman.h>
+#endif
+#include "open.h"
+#include "mmap.h"
+
+int mmap_unmap(char* mapped,unsigned long maplen) {
+#ifdef __MINGW32__
+  (void)maplen;
+  return UnmapViewOfFile(mapped)?0:-1;
+#else
+  return munmap(mapped,maplen);
+#endif
+}