diff --git a/darwin/opentype.m b/darwin/opentype.m
index 1a2f3ab1..890aa02a 100644
--- a/darwin/opentype.m
+++ b/darwin/opentype.m
@@ -51,7 +51,8 @@ void uiOpenTypeFeaturesRemove(uiOpenTypeFeatures *otf, char a, char b, char c, c
 	[otf->tags removeObjectForKey:tn];
 }
 
-int uiOpenTypeFeaturesGet(uiOpenTypeFeatures *otf, char a, char b, char c, char d, uint32_t *value)
+// TODO will the const wreck stuff up?
+int uiOpenTypeFeaturesGet(const uiOpenTypeFeatures *otf, char a, char b, char c, char d, uint32_t *value)
 {
 	NSNumber *tn, *vn;
 
@@ -78,7 +79,7 @@ void uiOpenTypeFeaturesForEach(const uiOpenTypeFeatures *otf, uiOpenTypeFeatures
 		b = (uint8_t) ((tag >> 16) & 0xFF);
 		c = (uint8_t) ((tag >> 8) & 0xFF);
 		d = (uint8_t) (tag & 0xFF);
-		ret = (*f)((char) a, (char) b, (char) c, (char) d,
+		ret = (*f)(otf, (char) a, (char) b, (char) c, (char) d,
 			mapObjectValue(vn), data);
 		// TODO for all: require exact match?
 		if (ret == uiForEachStop)
@@ -98,7 +99,7 @@ int uiOpenTypeFeaturesEqual(const uiOpenTypeFeatures *a, const uiOpenTypeFeature
 // TODO explain all this
 // TODO rename outerArray and innerDict (the names made sense when this was part of fontdescAppendFeatures(), but not here)
 // TODO make all this use enumerateKeysAndObjects (which requires duplicating code)?
-static uiForEach otfArrayForEachAAT(char a, char b, char c, char d, uint32_t value, void *data)
+static uiForEach otfArrayForEachAAT(const uiOpenTypeFeatures *otf, char a, char b, char c, char d, uint32_t value, void *data)
 {
 	CFMutableArrayRef outerArray = (CFMutableArrayRef) data;
 
@@ -133,7 +134,7 @@ static uiForEach otfArrayForEachAAT(char a, char b, char c, char d, uint32_t val
 }
 
 // TODO find out which fonts differ in AAT small caps and test them with this
-static uiForEach otfArrayForEachOT(char a, char b, char c, char d, uint32_t value, void *data)
+static uiForEach otfArrayForEachOT(const uiOpenTypeFeatures *otf, char a, char b, char c, char d, uint32_t value, void *data)
 {
 	CFMutableArrayRef outerArray = (CFMutableArrayRef) data;
 	CFDictionaryRef innerDict;
diff --git a/ui.h b/ui.h
index 1a875cab..039d45f4 100644
--- a/ui.h
+++ b/ui.h
@@ -4,6 +4,7 @@
 
 // TODOs
 // - make getters that return whether something exists accept a NULL pointer to discard the value (and thus only return that the thing exists?)
+// - const-correct everything
 
 #ifndef __LIBUI_UI_H__
 #define __LIBUI_UI_H__
diff --git a/ui_attrstr.h b/ui_attrstr.h
index 835cee39..430d65d0 100644
--- a/ui_attrstr.h
+++ b/ui_attrstr.h
@@ -104,8 +104,10 @@ _UI_ENUM(uiDrawUnderlineColor) {
 // TODO invalid features
 typedef struct uiOpenTypeFeatures uiOpenTypeFeatures;
 
-// TODO pass the feature set? (resolve const struct issue below first)
-typedef uiForEach (*uiOpenTypeFeaturesForEachFunc)(char a, char b, char c, char d, uint32_t value, void *data);
+// uiOpenTypeFeaturesForEachFunc is the type of the function
+// invoked by uiOpenTypeFeaturesForEach() for every OpenType
+// feature in otf.
+typedef uiForEach (*uiOpenTypeFeaturesForEachFunc)(const uiOpenTypeFeatures *otf, char a, char b, char c, char d, uint32_t value, void *data);
 
 // @role uiOpenTypeFeatures constructor
 // uiNewOpenTypeFeatures() returns a new uiOpenTypeFeatures
@@ -143,12 +145,11 @@ _UI_EXTERN void uiOpenTypeFeaturesRemove(uiOpenTypeFeatures *otf, char a, char b
 // for a feature. You should likewise not treat a missing feature as
 // having a value of zero either. Instead, a missing feature should
 // be treated as having some unspecified default value.
-// TODO const-correct this function (can we do that given the members of the struct on some platforms being full blown objects that may or may not themselves be const-correct?)
-_UI_EXTERN int uiOpenTypeFeaturesGet(uiOpenTypeFeatures *otf, char a, char b, char c, char d, uint32_t *value);
+_UI_EXTERN int uiOpenTypeFeaturesGet(const uiOpenTypeFeatures *otf, char a, char b, char c, char d, uint32_t *value);
 
 // uiOpenTypeFeaturesForEach() executes f for every tag-value
-// pair in otf. The enumeration order is unspecified.
-// TODO make other enumerators const (and in general const-correct everything) (but see the const struct TODO below and the const struct object member TODO above)
+// pair in otf. The enumeration order is unspecified. You cannot
+// modify otf while uiOpenTypeFeaturesForEach() is running.
 _UI_EXTERN void uiOpenTypeFeaturesForEach(const uiOpenTypeFeatures *otf, uiOpenTypeFeaturesForEachFunc f, void *data);
 
 // uiOpenTypeFeaturesEqual() returns nonzero if a is equal to b.
diff --git a/unix/opentype.c b/unix/opentype.c
index 764da50a..30933ea8 100644
--- a/unix/opentype.c
+++ b/unix/opentype.c
@@ -60,9 +60,8 @@ void uiOpenTypeFeaturesRemove(uiOpenTypeFeatures *otf, char a, char b, char c, c
 	g_hash_table_remove(otf->tags, mkTag(a, b, c, d));
 }
 
-// TODO should this be before Add and Remove?
-// TODO better name than Get?
-int uiOpenTypeFeaturesGet(uiOpenTypeFeatures *otf, char a, char b, char c, char d, uint32_t *value)
+// TODO will the const wreck stuff up?
+int uiOpenTypeFeaturesGet(const uiOpenTypeFeatures *otf, char a, char b, char c, char d, uint32_t *value)
 {
 	gboolean found;
 	gpointer gv;
@@ -77,6 +76,7 @@ int uiOpenTypeFeaturesGet(uiOpenTypeFeatures *otf, char a, char b, char c, char
 }
 
 struct otfForEach {
+	const uiOpenTypeFeatures *otf;
 	uiOpenTypeFeaturesForEachFunc f;
 	void *data;
 	uiForEach ret;
@@ -96,7 +96,7 @@ static void foreach(gpointer key, gpointer value, gpointer data)
 	b = (uint8_t) ((tag >> 16) & 0xFF);
 	c = (uint8_t) ((tag >> 8) & 0xFF);
 	d = (uint8_t) (tag & 0xFF);
-	ofe->ret = (*(ofe->f))((char) a, (char) b, (char) c, (char) d, GPOINTER_TO_INT(value), ofe->data);
+	ofe->ret = (*(ofe->f))(ofe->otf, (char) a, (char) b, (char) c, (char) d, GPOINTER_TO_INT(value), ofe->data);
 }
 
 void uiOpenTypeFeaturesForEach(const uiOpenTypeFeatures *otf, uiOpenTypeFeaturesForEachFunc f, void *data)
@@ -104,6 +104,7 @@ void uiOpenTypeFeaturesForEach(const uiOpenTypeFeatures *otf, uiOpenTypeFeatures
 	struct otfForEach ofe;
 
 	memset(&ofe, 0, sizeof (struct otfForEach));
+	ofe.otf = otf;
 	ofe.f = f;
 	ofe.data = data;
 	g_hash_table_foreach(otf->tags, foreach, &ofe);
@@ -183,7 +184,7 @@ out:
 
 // see https://developer.mozilla.org/en/docs/Web/CSS/font-feature-settings
 // TODO make this a g_hash_table_foreach() function (which requires duplicating code)?
-static uiForEach toCSS(char a, char b, char c, char d, uint32_t value, void *data)
+static uiForEach toCSS(const uiOpenTypeFeatures *otf, char a, char b, char c, char d, uint32_t value, void *data)
 {
 	// TODO is there a G_STRING()?
 	GString *s = (GString *) data;
diff --git a/windows/opentype.cpp b/windows/opentype.cpp
index 8fc37175..235f0388 100644
--- a/windows/opentype.cpp
+++ b/windows/opentype.cpp
@@ -45,7 +45,8 @@ void uiOpenTypeFeaturesRemove(uiOpenTypeFeatures *otf, char a, char b, char c, c
 	otf->tags->erase(mktag(a, b, c, d));
 }
 
-int uiOpenTypeFeaturesGet(uiOpenTypeFeatures *otf, char a, char b, char c, char d, uint32_t *value)
+// TODO will the const wreck stuff up?
+int uiOpenTypeFeaturesGet(const uiOpenTypeFeatures *otf, char a, char b, char c, char d, uint32_t *value)
 {
 	tagmap::const_iterator iter;
 
@@ -69,7 +70,7 @@ void uiOpenTypeFeaturesForEach(const uiOpenTypeFeatures *otf, uiOpenTypeFeatures
 		b = (uint8_t) ((iter->first >> 8) & 0xFF);
 		c = (uint8_t) ((iter->first >> 16) & 0xFF);
 		d = (uint8_t) ((iter->first >> 24) & 0xFF);
-		ret = (*f)((char) a, (char) b, (char) c, (char) d,
+		ret = (*f)(otf, (char) a, (char) b, (char) c, (char) d,
 			iter->second, data);
 		if (ret == uiForEachStop)
 			return;