diff --git a/mmap.h b/mmap.h
index bd95d16..53ea10e 100644
--- a/mmap.h
+++ b/mmap.h
@@ -22,7 +22,7 @@ char* mmap_private(const char *filename,size_t* filesize);
 char* mmap_shared(const char *filename,size_t* filesize);
 
 /* unmap a mapped region */
-int mmap_unmap(char* mapped,size_t maplen);
+int mmap_unmap(const char* mapped,size_t maplen);
 
 #ifdef __cplusplus
 }
diff --git a/mmap/mmap_unmap.c b/mmap/mmap_unmap.c
index dd0030f..994e486 100644
--- a/mmap/mmap_unmap.c
+++ b/mmap/mmap_unmap.c
@@ -8,11 +8,11 @@
 #include "open.h"
 #include "mmap.h"
 
-int mmap_unmap(char* mapped,size_t maplen) {
+int mmap_unmap(const char* mapped,size_t maplen) {
 #ifdef __MINGW32__
   (void)maplen;
   return UnmapViewOfFile(mapped)?0:-1;
 #else
-  return munmap(mapped,maplen);
+  return munmap((char*)mapped,maplen);
 #endif
 }