diff --git a/stylesheets.rs b/stylesheets.rs
index 0f7f275ef01..12d71ecc525 100644
--- a/stylesheets.rs
+++ b/stylesheets.rs
@@ -10,10 +10,11 @@ use properties;
 use errors::{ErrorLoggerIterator, log_css_error};
 use namespaces::{NamespaceMap, parse_namespace_rule};
 use media_queries::{MediaRule, parse_media_rule};
+use media_queries;
 
 
 pub struct Stylesheet {
-    style_rules: ~[CSSRule],
+    rules: ~[CSSRule],
     namespaces: NamespaceMap,
 }
 
@@ -88,7 +89,7 @@ fn parse_stylesheet(css: &str) -> Stylesheet {
         }
         state = next_state;
     }
-    Stylesheet{ style_rules: rules, namespaces: namespaces }
+    Stylesheet{ rules: rules, namespaces: namespaces }
 }
 
 
@@ -113,3 +114,39 @@ pub fn parse_nested_at_rule(lower_name: &str, rule: AtRule,
         _ => log_css_error(rule.location, fmt!("Unsupported at-rule: @%s", lower_name))
     }
 }
+
+
+impl Stylesheet {
+    fn iter_style_rules<'a>(&'a self, device: media_queries::Device) -> StyleRuleIterator<'a> {
+        StyleRuleIterator { device: device, stack: ~[(self.rules.as_slice(), 0)] }
+    }
+}
+
+struct StyleRuleIterator<'self> {
+    device: media_queries::Device,
+    // FIXME: I couldn’t get this to borrow-check with a stack of VecIterator
+    stack: ~[(&'self [CSSRule], uint)],
+}
+
+impl<'self> Iterator<&'self StyleRule> for StyleRuleIterator<'self> {
+    fn next(&mut self) -> Option<&'self StyleRule> {
+        loop {
+            match self.stack.pop_opt() {
+                None => return None,
+                Some((rule_list, i)) => {
+                    if i + 1 < rule_list.len() {
+                        self.stack.push((rule_list, i + 1))
+                    }
+                    match rule_list[i] {
+                        CSSStyleRule(ref rule) => return Some(rule),
+                        CSSMediaRule(ref rule) => {
+                            if rule.media_queries.evaluate(&self.device) {
+                                self.stack.push((rule.rules.as_slice(), 0))
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+}