diff --git a/src/hb-common.cc b/src/hb-common.cc
index 7c6d262..666d77d 100644
--- a/src/hb-common.cc
+++ b/src/hb-common.cc
@@ -187,7 +187,7 @@
     return *this;
   }
 
-  void finish (void) { free (lang); }
+  void finish (void) { free ((void *) lang); }
 };
 
 
diff --git a/src/hb-common.h b/src/hb-common.h
index 9079b2c..40c1887 100644
--- a/src/hb-common.h
+++ b/src/hb-common.h
@@ -131,7 +131,7 @@
 
 /* hb_language_t */
 
-typedef struct hb_language_impl_t *hb_language_t;
+typedef const struct hb_language_impl_t *hb_language_t;
 
 /* len=-1 means str is NUL-terminated */
 hb_language_t