diff --git a/darwin/opentype.m b/darwin/opentype.m
index 25939299..52db9560 100644
--- a/darwin/opentype.m
+++ b/darwin/opentype.m
@@ -20,7 +20,7 @@ void uiFreeOpenTypeFeatures(uiOpenTypeFeatures *otf)
 	uiFree(otf);
 }
 
-uiOpenTypeFeatures *uiOpenTypeFeaturesClone(uiOpenTypeFeatures *otf)
+uiOpenTypeFeatures *uiOpenTypeFeaturesClone(const uiOpenTypeFeatures *otf)
 {
 	uiOpenTypeFeatures *out;
 
@@ -82,7 +82,7 @@ void uiOpenTypeFeaturesForEach(uiOpenTypeFeatures *otf, uiOpenTypeFeaturesForEac
 	}];
 }
 
-int uiOpenTypeFeaturesEqual(uiOpenTypeFeatures *a, uiOpenTypeFeatures *b)
+int uiOpenTypeFeaturesEqual(const uiOpenTypeFeatures *a, const uiOpenTypeFeatures *b)
 {
 	return [a->tags isEqualToDictionary:b->tags];
 }
diff --git a/unix/opentype.c b/unix/opentype.c
index 6ea317c5..6700b83e 100644
--- a/unix/opentype.c
+++ b/unix/opentype.c
@@ -28,7 +28,7 @@ static void cloneTags(gpointer key, gpointer value, gpointer data)
 	g_hash_table_replace((GHashTable *) data, key, value);
 }
 
-uiOpenTypeFeatures *uiOpenTypeFeaturesClone(uiOpenTypeFeatures *otf)
+uiOpenTypeFeatures *uiOpenTypeFeaturesClone(const uiOpenTypeFeatures *otf)
 {
 	uiOpenTypeFeatures *out;
 
@@ -119,10 +119,11 @@ static GList *copySortedKeys(GHashTable *tags)
 	copy = g_list_copy(k);
 	copy = g_list_sort(copy, tagcmp);
 	// TODO do we free k? the docs contradict themselves
+	// TODO I already forgot, does g_list_sort() copy, or just change the head?
 	return copy;
 }
 
-int uiOpenTypeFeaturesEqual(uiOpenTypeFeatures *a, uiOpenTypeFeatures *b)
+int uiOpenTypeFeaturesEqual(const uiOpenTypeFeatures *a, const uiOpenTypeFeatures *b)
 {
 	GList *ak, *bk;
 	GList *ai, *bi;
diff --git a/windows/opentype.cpp b/windows/opentype.cpp
index f3ca36c3..141f8a5f 100644
--- a/windows/opentype.cpp
+++ b/windows/opentype.cpp
@@ -22,7 +22,7 @@ void uiFreeOpenTypeFeatures(uiOpenTypeFeatures *otf)
 	uiFree(otf);
 }
 
-uiOpenTypeFeatures *uiOpenTypeFeaturesClone(uiOpenTypeFeatures *otf)
+uiOpenTypeFeatures *uiOpenTypeFeaturesClone(const uiOpenTypeFeatures *otf)
 {
 	uiOpenTypeFeatures *out;
 
@@ -75,7 +75,7 @@ void uiOpenTypeFeaturesForEach(uiOpenTypeFeatures *otf, uiOpenTypeFeaturesForEac
 	}
 }
 
-int uiOpenTypeFeaturesEqual(uiOpenTypeFeatures *a, uiOpenTypeFeatures *b)
+int uiOpenTypeFeaturesEqual(const uiOpenTypeFeatures *a, const uiOpenTypeFeatures *b)
 {
 	// TODO make sure this is correct
 	return *(a->tags) == *(b->tags);