diff --git a/hawk/lib/hawk-utl.h b/hawk/lib/hawk-utl.h
index 36579604..aaf0e2c7 100644
--- a/hawk/lib/hawk-utl.h
+++ b/hawk/lib/hawk-utl.h
@@ -694,15 +694,15 @@ HAWK_EXPORT hawk_oow_t hawk_rotate_bchars (
 );
 
 HAWK_EXPORT hawk_uch_t* hawk_trim_uchars (
-	hawk_uch_t* str,
-	hawk_oow_t* len,
-	int         flags
+	const hawk_uch_t* str,
+	hawk_oow_t*       len,
+	int               flags
 );
 
 HAWK_EXPORT hawk_bch_t* hawk_trim_bchars (
-	hawk_bch_t* str,
-	hawk_oow_t* len,
-	int         flags
+	const hawk_bch_t* str,
+	hawk_oow_t*       len,
+	int               flags
 );
 
 HAWK_EXPORT int hawk_split_ucstr (
diff --git a/hawk/lib/utl-str.c b/hawk/lib/utl-str.c
index 8562f446..b876d10c 100644
--- a/hawk/lib/utl-str.c
+++ b/hawk/lib/utl-str.c
@@ -942,9 +942,9 @@ hawk_oow_t hawk_rotate_bchars (hawk_bch_t* str, hawk_oow_t len, int dir, hawk_oo
 
 /* ------------------------------------------------------------------------ */
 
-hawk_uch_t* hawk_trim_uchars (hawk_uch_t* str, hawk_oow_t* len, int flags)
+hawk_uch_t* hawk_trim_uchars (const hawk_uch_t* str, hawk_oow_t* len, int flags)
 {
-	hawk_uch_t* p = str, * end = str + *len;
+	const hawk_uch_t* p = str, * end = str + *len;
 
 	if (p < end)
 	{
@@ -981,12 +981,12 @@ hawk_uch_t* hawk_trim_uchars (hawk_uch_t* str, hawk_oow_t* len, int flags)
 		}
 	}
 
-	return str;
+	return (hawk_uch_t*)str;
 }
 
-hawk_bch_t* hawk_trim_bchars (hawk_bch_t* str, hawk_oow_t* len, int flags)
+hawk_bch_t* hawk_trim_bchars (const hawk_bch_t* str, hawk_oow_t* len, int flags)
 {
-	hawk_bch_t* p = str, * end = str + *len;
+	const hawk_bch_t* p = str, * end = str + *len;
 
 	if (p < end)
 	{
@@ -1023,7 +1023,7 @@ hawk_bch_t* hawk_trim_bchars (hawk_bch_t* str, hawk_oow_t* len, int flags)
 		}
 	}
 
-	return str;
+	return (hawk_bch_t*)str;
 }
 /* ------------------------------------------------------------------------ */