diff --git a/include/filehandling.h b/include/filehandling.h
index 1d13097e4..db03ac456 100644
--- a/include/filehandling.h
+++ b/include/filehandling.h
@@ -15,8 +15,8 @@
 int    _wopen       (const char *path, int oflag, ...);
 #endif
 
-bool   hc_fopen     (HCFILE *fp, const char *path, char *mode);
-bool   hc_fopen_raw (HCFILE *fp, const char *path, char *mode);
+bool   hc_fopen     (HCFILE *fp, const char *path, const char *mode);
+bool   hc_fopen_raw (HCFILE *fp, const char *path, const char *mode);
 int    hc_fscanf    (HCFILE *fp, const char *format, void *ptr);
 int    hc_fprintf   (HCFILE *fp, const char *format, ...);
 int    hc_vfprintf  (HCFILE *fp, const char *format, va_list ap);
diff --git a/include/types.h b/include/types.h
index ed22a95ee..9b58e6c6a 100644
--- a/include/types.h
+++ b/include/types.h
@@ -1075,7 +1075,7 @@ typedef struct hc_fp
   bool        is_zip;
   int         bom_size;
 
-  char       *mode;
+  const char *mode;
   const char *path;
 
 } HCFILE;
diff --git a/src/filehandling.c b/src/filehandling.c
index 54ba73369..9edd1cb35 100644
--- a/src/filehandling.c
+++ b/src/filehandling.c
@@ -21,7 +21,7 @@ int _wopen (const char *path, int oflag, ...)
 }
 #endif
 
-bool hc_fopen (HCFILE *fp, const char *path, char *mode)
+bool hc_fopen (HCFILE *fp, const char *path, const char *mode)
 {
   if (path == NULL || mode == NULL) return false;
 
@@ -130,7 +130,7 @@ bool hc_fopen (HCFILE *fp, const char *path, char *mode)
   return true;
 }
 
-bool hc_fopen_raw (HCFILE *fp, const char *path, char *mode)
+bool hc_fopen_raw (HCFILE *fp, const char *path, const char *mode)
 {
   if (path == NULL || mode == NULL) return false;