diff --git a/mio/lib/mio-utl.h b/mio/lib/mio-utl.h
index 9fcffa1..da99392 100644
--- a/mio/lib/mio-utl.h
+++ b/mio/lib/mio-utl.h
@@ -469,18 +469,17 @@ MIO_EXPORT mio_bch_t* mio_find_bchar_in_bcstr (
 );
 
 MIO_EXPORT mio_uch_t* mio_trim_uchars (
-	mio_uch_t* str,
-	mio_oow_t* len,
-	int        flags
+	const mio_uch_t* str,
+	mio_oow_t*       len,
+	int              flags
 );
 
 MIO_EXPORT mio_bch_t* mio_trim_bchars (
-	mio_bch_t* str,
-	mio_oow_t* len,
-	int        flags
+	const mio_bch_t* str,
+	mio_oow_t*       len,
+	int              flags
 );
 
-
 MIO_EXPORT int mio_split_ucstr (
 	mio_uch_t*       s,
 	const mio_uch_t* delim,
diff --git a/mio/lib/utl.c b/mio/lib/utl.c
index fc3678f..69fd591 100644
--- a/mio/lib/utl.c
+++ b/mio/lib/utl.c
@@ -639,9 +639,9 @@ const mio_uch_t* mio_find_ucstr_word_in_ucstr (const mio_uch_t* str, const mio_u
 
 /* ========================================================================= */
 
-mio_uch_t* mio_trim_uchars (mio_uch_t* str, mio_oow_t* len, int flags)
+mio_uch_t* mio_trim_uchars (const mio_uch_t* str, mio_oow_t* len, int flags)
 {
-	mio_uch_t* p = str, * end = str + *len;
+	const mio_uch_t* p = str, * end = str + *len;
 
 	if (p < end)
 	{
@@ -678,12 +678,12 @@ mio_uch_t* mio_trim_uchars (mio_uch_t* str, mio_oow_t* len, int flags)
 		}
 	}
 
-	return str;
+	return (mio_uch_t*)str;
 }
 
-mio_bch_t* mio_trim_bchars (mio_bch_t* str, mio_oow_t* len, int flags)
+mio_bch_t* mio_trim_bchars (const mio_bch_t* str, mio_oow_t* len, int flags)
 {
-	mio_bch_t* p = str, * end = str + *len;
+	const mio_bch_t* p = str, * end = str + *len;
 
 	if (p < end)
 	{
@@ -720,7 +720,7 @@ mio_bch_t* mio_trim_bchars (mio_bch_t* str, mio_oow_t* len, int flags)
 		}
 	}
 
-	return str;
+	return (mio_bch_t*)str;
 }
 
 /* ========================================================================= */