diff --git a/font-renderer/src/directwrite/mod.rs b/font-renderer/src/directwrite/mod.rs
index 86ec3c57..fd16678f 100644
--- a/font-renderer/src/directwrite/mod.rs
+++ b/font-renderer/src/directwrite/mod.rs
@@ -22,6 +22,7 @@ use std::iter::Cloned;
 use std::mem;
 use std::os::raw::c_void;
 use std::ptr;
+use std::collections::btree_map::Entry;
 use std::slice::{self, Iter};
 use std::sync::Arc;
 use uuid::IID_ID2D1SimplifiedGeometrySink;
@@ -36,7 +37,8 @@ use winapi::{IDWriteFontFileLoader, IDWriteFontFileLoaderVtbl, IDWriteFontFileSt
 use winapi::{IDWriteFontFileStreamVtbl, IDWriteGeometrySink, IUnknown, IUnknownVtbl, TRUE, UINT16};
 use winapi::{UINT32, UINT64, UINT};
 
-use self::com::{PathfinderCoclass, PathfinderComObject, PathfinderComPtr};
+use self::com::{PathfinderCoclass, PathfinderComObject};
+pub use self::com::{PathfinderComPtr};
 use {FontInstance, GlyphDimensions, GlyphImage, GlyphKey};
 
 mod com;
@@ -178,6 +180,19 @@ impl<FK> FontContext<FK> where FK: Clone + Hash + Eq + Ord {
         }
     }
 
+    /// Loads an OpenType font from a COM `IDWriteFontFace` handle.
+    pub fn add_native_font<H>(&mut self, font_key: &FK, handle: H) -> Result<(), ()> 
+                        where H: Into<PathfinderComPtr<IDWriteFontFace>>
+    {
+        match self.dwrite_font_faces.entry((*font_key).clone()) {
+            Entry::Occupied(_) => Ok(()),
+            Entry::Vacant(entry) => {
+                entry.insert(handle.into());
+                Ok(())
+            }
+        }
+    }
+
     /// Unloads the font with the given font key from memory.
     /// 
     /// If the font isn't loaded, does nothing.
@@ -193,11 +208,14 @@ impl<FK> FontContext<FK> where FK: Clone + Hash + Eq + Ord {
     /// libraries (including Pathfinder) apply modifications to the outlines: for example, to
     /// dilate them for easier reading. To retrieve extents that account for these modifications,
     /// set `exact` to false.
-    pub fn glyph_dimensions(&self, font_instance: &FontInstance<FK>, glyph_key: &GlyphKey)
-                            -> Option<GlyphDimensions> {
+    pub fn glyph_dimensions(&self,
+                            font_instance: &FontInstance<FK>,
+                            glyph_key: &GlyphKey,
+                            _exact: bool)
+                            -> Result<GlyphDimensions, ()> {
         unsafe {
             let font_face = match self.dwrite_font_faces.get(&font_instance.font_key) {
-                None => return None,
+                None => return Err(()),
                 Some(font_face) => (*font_face).clone(),
             };
 
@@ -206,10 +224,10 @@ impl<FK> FontContext<FK> where FK: Clone + Hash + Eq + Ord {
 
             let result = (**font_face).GetDesignGlyphMetrics(&glyph_index, 1, &mut metrics, FALSE);
             if !winerror::SUCCEEDED(result) {
-                return None
+                return Err(());
             }
 
-            Some(GlyphDimensions {
+            Ok(GlyphDimensions {
                 advance: metrics.advanceWidth as f32,
                 origin: Point2D::new(metrics.leftSideBearing, metrics.bottomSideBearing),
                 size: Size2D::new((metrics.rightSideBearing - metrics.leftSideBearing) as u32,
diff --git a/font-renderer/src/lib.rs b/font-renderer/src/lib.rs
index cce5471e..60aedb65 100644
--- a/font-renderer/src/lib.rs
+++ b/font-renderer/src/lib.rs
@@ -53,6 +53,11 @@ extern crate uuid;
 #[macro_use(DEFINE_GUID)]
 extern crate winapi;
 
+#[cfg(target_os = "windows")]
+pub use self::directwrite::PathfinderComPtr;
+#[cfg(target_os = "windows")]
+pub use winapi::IDWriteFontFace;
+
 use app_units::Au;
 use euclid::{Point2D, Size2D};