diff --git a/complete.rs b/complete.rs
index 4b2af32..77c0a8e 100644
--- a/complete.rs
+++ b/complete.rs
@@ -7,6 +7,7 @@ use color::Color;
 use select::SelectResults;
 use computed::ComputedStyle;
 use n::h::CssHintLength;
+use n::c::ComputeFontSize;
 use n::u::float_to_css_fixed;
 use values::*;
 use n;
@@ -15,6 +16,16 @@ pub struct CompleteSelectResults {
     inner: SelectResults
 }
 
+struct ComputeFontSizeCallback {
+    callback: ~fn(parent: &Option<n::h::CssHint>, child: &n::h::CssHint) -> n::h::CssHint,
+}
+
+impl ComputeFontSize for ComputeFontSizeCallback {
+    fn compute_font_size(&self, parent: &Option<n::h::CssHint>, child: &n::h::CssHint) -> n::h::CssHint {
+        (self.callback)(parent, child)
+    }
+}
+
 impl<'self> CompleteSelectResults {
     pub fn new_root(root: SelectResults) -> CompleteSelectResults {
         CompleteSelectResults {
@@ -31,42 +42,43 @@ impl<'self> CompleteSelectResults {
             //let net_parent_computed = &parent_computed.inner.inner;
             let net_child_computed = &/*mut*/ child_computed.inner;
             // FIXME: Need to get real font sizes
-            let cb: n::c::ComputeFontSizeCb =
-                |parent: &Option<n::h::CssHint>, child: &n::h::CssHint| -> n::h::CssHint {
-                match *child {
-                    // Handle relative units
-                    CssHintLength(n::t::CssUnitEm(child_em)) => {
-                        match *parent {
-                            Some(CssHintLength(parent_unit)) => {
-                                // CSS3 Values 5.1.1: Multiply parent unit by child unit.
-                                let mut new_value =
-                                    n::u::css_fixed_to_float(parent_unit.to_css_fixed());
-                                new_value *= n::u::css_fixed_to_float(child_em);
-                                let unit = parent_unit.modify(n::u::float_to_css_fixed(
-                                    new_value));
-                                CssHintLength(unit)
+            let cb = @ComputeFontSizeCallback {
+                callback: |parent: &Option<n::h::CssHint>, child: &n::h::CssHint| -> n::h::CssHint {
+                    match *child {
+                        // Handle relative units
+                        CssHintLength(n::t::CssUnitEm(child_em)) => {
+                            match *parent {
+                                Some(CssHintLength(parent_unit)) => {
+                                    // CSS3 Values 5.1.1: Multiply parent unit by child unit.
+                                    let mut new_value =
+                                        n::u::css_fixed_to_float(parent_unit.to_css_fixed());
+                                    new_value *= n::u::css_fixed_to_float(child_em);
+                                    let unit = parent_unit.modify(n::u::float_to_css_fixed(
+                                        new_value));
+                                    CssHintLength(unit)
+                                }
+                                _ => n::h::CssHintLength(n::t::CssUnitPx(float_to_css_fixed(16.0))),
                             }
-                            _ => n::h::CssHintLength(n::t::CssUnitPx(float_to_css_fixed(16.0))),
                         }
-                    }
-                    CssHintLength(n::t::CssUnitPct(child_pct)) => {
-                        match *parent {
-                            Some(CssHintLength(parent_unit)) => {
-                                // CSS3 Values 5.1.1: Multiply parent unit by child unit.
-                                let mut new_value =
-                                    n::u::css_fixed_to_float(parent_unit.to_css_fixed());
-                                new_value *= n::u::css_fixed_to_float(child_pct) / 100.0;
-                                let unit = parent_unit.modify(n::u::float_to_css_fixed(
-                                    new_value));
-                                CssHintLength(unit)
+                        CssHintLength(n::t::CssUnitPct(child_pct)) => {
+                            match *parent {
+                                Some(CssHintLength(parent_unit)) => {
+                                    // CSS3 Values 5.1.1: Multiply parent unit by child unit.
+                                    let mut new_value =
+                                        n::u::css_fixed_to_float(parent_unit.to_css_fixed());
+                                    new_value *= n::u::css_fixed_to_float(child_pct) / 100.0;
+                                    let unit = parent_unit.modify(n::u::float_to_css_fixed(
+                                        new_value));
+                                    CssHintLength(unit)
+                                }
+                                _ => n::h::CssHintLength(n::t::CssUnitPx(float_to_css_fixed(16.0))),
                             }
-                            _ => n::h::CssHintLength(n::t::CssUnitPx(float_to_css_fixed(16.0))),
                         }
-                    }
-                    // Pass through absolute units
-                    CssHintLength(unit) => CssHintLength(unit),
-                    _ => {
-                        n::h::CssHintLength(n::t::CssUnitPx(float_to_css_fixed(16.0)))
+                        // Pass through absolute units
+                        CssHintLength(unit) => CssHintLength(unit),
+                        _ => {
+                            n::h::CssHintLength(n::t::CssUnitPx(float_to_css_fixed(16.0)))
+                        }
                     }
                 }
             };
@@ -74,7 +86,7 @@ impl<'self> CompleteSelectResults {
             let net_result_computed: &mut n::c::CssComputedStyle = unsafe { cast::transmute(net_child_computed) };
             let net_child_computed: &mut n::c::CssComputedStyle = unsafe { cast::transmute(&child_computed.inner) };
             let net_parent_computed = &parent_computed.inner.inner;
-            n::c::compose(net_parent_computed, net_child_computed, cb, net_result_computed);
+            n::c::compose(net_parent_computed, net_child_computed, cb as @ComputeFontSize, net_result_computed);
         }
 
         CompleteSelectResults {
diff --git a/test.rs b/test.rs
index 40e5655..005a395 100644
--- a/test.rs
+++ b/test.rs
@@ -3,7 +3,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use extra::url::Url;
-use std::FromStr;
 use std::cast;
 use std::libc;
 use std::cell::Cell;
diff --git a/util.rs b/util.rs
index dce59a3..efeb67d 100644
--- a/util.rs
+++ b/util.rs
@@ -4,4 +4,4 @@
 
 pub use netsurfcss::util::VoidPtrLike;
 
-pub type DataStream = @fn() -> Option<~[u8]>;
+pub type DataStream = ~fn() -> Option<~[u8]>;