diff --git a/fisdir.c b/fisdir.c
index d9d7b68..8f8a28c 100644
--- a/fisdir.c
+++ b/fisdir.c
@@ -32,7 +32,7 @@
  * Returns:
  * %TRUE(1) if the file exists and is a directory, otherwise %FALSE(0).
  */
-int fisdir(char *file)
+int fisdir(const char *file)
 {
 	struct stat sb;
 
diff --git a/lite.h b/lite.h
index 74786b1..7168930 100644
--- a/lite.h
+++ b/lite.h
@@ -39,7 +39,7 @@ typedef struct lfile lfile_t;
 char   *chomp      (char *str);
 
 int     fexist     (char *file);
-int     fisdir     (char *file);
+int     fisdir     (const char *file);
 mode_t  fmode      (char *file);
 
 FILE   *tempfile   (void);