diff --git a/utils/path.c b/utils/path.c
index d82dbb55..26c678f2 100644
--- a/utils/path.c
+++ b/utils/path.c
@@ -80,7 +80,7 @@ bool FileLocking = TRUE;
  
 char *
 PaCheckCompressed(filename)
-    char *filename;
+    const char *filename;
 {
     int fd;
     char *gzname;
diff --git a/utils/utils.h b/utils/utils.h
index b51cb12d..d3ece6d8 100644
--- a/utils/utils.h
+++ b/utils/utils.h
@@ -77,7 +77,7 @@ extern bool ParsSplit();
 #ifdef HAVE_ZLIB
 extern gzFile PaZOpen(char *, char *, char *, char *, char *, char **);
 extern gzFile PaLockZOpen(char *, char *, char *, char *, char *, char **, bool *, int *);
-extern char *PaCheckCompressed(char *);
+extern char *PaCheckCompressed(const char *filename);
 #endif
 
 extern int SetNoisyBool(bool *, char *, FILE *);