--- a/servo/components/style/gecko_bindings/sugar/mod.rs
+++ b/servo/components/style/gecko_bindings/sugar/mod.rs
@@ -1,12 +1,13 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 mod ns_com_ptr;
 mod ns_css_shadow_array;
 mod ns_style_auto_array;
 pub mod ns_style_coord;
+mod ns_timing_function;
 mod ns_t_array;
 pub mod ownership;
 pub mod refptr;
 mod style_complex_color;

new file mode 100644
--- /dev/null
+++ b/servo/components/style/gecko_bindings/sugar/ns_timing_function.rs
@@ -0,0 +1,69 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use euclid::point::TypedPoint2D;
+use gecko_bindings::structs::{nsTimingFunction, nsTimingFunction_Type};
+use properties::longhands::animation_timing_function::computed_value::{StartEnd, TransitionTimingFunction};
+use std::mem;
+
+impl From<TransitionTimingFunction > for nsTimingFunction {
+    fn from(function: TransitionTimingFunction) -> nsTimingFunction {
+        let mut tf: nsTimingFunction = unsafe { mem::zeroed() };
+
+        match function {
+            TransitionTimingFunction::Steps(steps, StartEnd::Start) => {
+                tf.mType = nsTimingFunction_Type::StepStart;
+                unsafe {
+                    tf.__bindgen_anon_1.__bindgen_anon_1.as_mut().mSteps = steps;
+                }
+            },
+            TransitionTimingFunction::Steps(steps, StartEnd::End) => {
+                tf.mType = nsTimingFunction_Type::StepEnd;
+                unsafe {
+                    tf.__bindgen_anon_1.__bindgen_anon_1.as_mut().mSteps = steps;
+                }
+            },
+            TransitionTimingFunction::CubicBezier(p1, p2) => {
+                tf.mType = nsTimingFunction_Type::CubicBezier;
+                let ref mut gecko_cubic_bezier =
+                    unsafe { tf.__bindgen_anon_1.mFunc.as_mut() };
+                gecko_cubic_bezier.mX1 = p1.x;
+                gecko_cubic_bezier.mY1 = p1.y;
+                gecko_cubic_bezier.mX2 = p2.x;
+                gecko_cubic_bezier.mY2 = p2.y;
+            },
+            // FIXME: we need to add more types once TransitionTimingFunction
+            // has more types.
+        }
+        tf
+    }
+}
+
+impl From<nsTimingFunction> for TransitionTimingFunction {
+    fn from(function: nsTimingFunction) -> TransitionTimingFunction {
+        match function.mType {
+            nsTimingFunction_Type::StepStart => {
+                TransitionTimingFunction::Steps(unsafe { function.__bindgen_anon_1.__bindgen_anon_1.as_ref().mSteps },
+                                                StartEnd::Start)
+            },
+            nsTimingFunction_Type::StepEnd => {
+                TransitionTimingFunction::Steps(unsafe { function.__bindgen_anon_1.__bindgen_anon_1.as_ref().mSteps },
+                                                StartEnd::End)
+            },
+            // FIXME: As above, we need to fix here.
+            nsTimingFunction_Type::Ease |
+            nsTimingFunction_Type::Linear |
+            nsTimingFunction_Type::EaseIn |
+            nsTimingFunction_Type::EaseOut |
+            nsTimingFunction_Type::EaseInOut |
+            nsTimingFunction_Type::CubicBezier => {
+                TransitionTimingFunction::CubicBezier(
+                    TypedPoint2D::new(unsafe { function.__bindgen_anon_1.mFunc.as_ref().mX1 },
+                                      unsafe { function.__bindgen_anon_1.mFunc.as_ref().mY1 }),
+                    TypedPoint2D::new(unsafe { function.__bindgen_anon_1.mFunc.as_ref().mX2 },
+                                      unsafe { function.__bindgen_anon_1.mFunc.as_ref().mY2 }))
+            },
+        }
+    }
+}