diff --git a/components/style/invalidation/element/invalidation_map.rs b/components/style/invalidation/element/invalidation_map.rs
index 4a1a092a2aa..58d612af122 100644
--- a/components/style/invalidation/element/invalidation_map.rs
+++ b/components/style/invalidation/element/invalidation_map.rs
@@ -15,7 +15,7 @@ use selectors::parser::{Selector, SelectorIter, SelectorMethods};
 use selectors::visitor::SelectorVisitor;
 use smallvec::SmallVec;
 #[cfg(feature = "gecko")]
-use stylesheets::{MallocEnclosingSizeOfFn, MallocSizeOfHash};
+use stylesheets::{MallocEnclosingSizeOfFn, MallocSizeOfFn, MallocSizeOfHash, MallocSizeOfVec};
 
 #[cfg(feature = "gecko")]
 /// Gets the element state relevant to the given `:dir` pseudo-class selector.
@@ -292,19 +292,29 @@ impl InvalidationMap {
 
     /// Measures heap usage.
     #[cfg(feature = "gecko")]
-    pub fn malloc_size_of_children(&self, malloc_enclosing_size_of: MallocEnclosingSizeOfFn)
+    pub fn malloc_size_of_children(&self, malloc_size_of: MallocSizeOfFn,
+                                   malloc_enclosing_size_of: MallocEnclosingSizeOfFn)
                                    -> usize {
         // Currently we measure the HashMap storage, but not things pointed to
         // by keys and values.
         let mut n = 0;
 
         n += self.class_to_selector.malloc_shallow_size_of_hash(malloc_enclosing_size_of);
-        n += self.id_to_selector.malloc_shallow_size_of_hash(malloc_enclosing_size_of);
+        for (_, val) in self.class_to_selector.iter() {
+            n += val.malloc_shallow_size_of_vec(malloc_size_of);
+        }
 
-        n += self.state_affecting_selectors.malloc_size_of_children(malloc_enclosing_size_of);
+        n += self.id_to_selector.malloc_shallow_size_of_hash(malloc_enclosing_size_of);
+        for (_, val) in self.id_to_selector.iter() {
+            n += val.malloc_shallow_size_of_vec(malloc_size_of);
+        }
+
+        n += self.state_affecting_selectors.malloc_size_of_children(malloc_size_of,
+                                                                    malloc_enclosing_size_of);
 
         n += self.other_attribute_affecting_selectors.malloc_size_of_children(
-            malloc_enclosing_size_of);
+            malloc_size_of, malloc_enclosing_size_of);
+
         n
     }
 }
diff --git a/components/style/selector_map.rs b/components/style/selector_map.rs
index 284b1a0a55f..cd96aa736d8 100644
--- a/components/style/selector_map.rs
+++ b/components/style/selector_map.rs
@@ -20,7 +20,7 @@ use selectors::parser::{Component, Combinator, SelectorIter};
 use smallvec::{SmallVec, VecLike};
 use std::hash::{BuildHasherDefault, Hash, Hasher};
 #[cfg(feature = "gecko")]
-use stylesheets::{MallocEnclosingSizeOfFn, MallocSizeOfHash};
+use stylesheets::{MallocEnclosingSizeOfFn, MallocSizeOfFn, MallocSizeOfHash, MallocSizeOfVec};
 use stylist::Rule;
 
 /// A hasher implementation that doesn't hash anything, because it expects its
@@ -149,16 +149,31 @@ impl<T: 'static> SelectorMap<T> {
 
     /// Measures heap usage.
     #[cfg(feature = "gecko")]
-    pub fn malloc_size_of_children(&self, malloc_enclosing_size_of: MallocEnclosingSizeOfFn)
+    pub fn malloc_size_of_children(&self, malloc_size_of: MallocSizeOfFn,
+                                   malloc_enclosing_size_of: MallocEnclosingSizeOfFn)
                                    -> usize {
-        // Currently we measure the HashMap storage, but not things pointed to
-        // by keys and values.
-        let mut n = 0;
-        n += self.id_hash.malloc_shallow_size_of_hash(malloc_enclosing_size_of);
-        n += self.class_hash.malloc_shallow_size_of_hash(malloc_enclosing_size_of);
-        n += self.local_name_hash.malloc_shallow_size_of_hash(malloc_enclosing_size_of);
+        // Currently we measure the storage used by the HashMaps, and any
+        // heap-allocated SmallVec values, but not things pointed to by the T
+        // elements within the SmallVec values.
 
-        // We may measure other fields in the future if DMD says it's worth it.
+        let mut n = 0;
+
+        n += self.id_hash.malloc_shallow_size_of_hash(malloc_enclosing_size_of);
+        for (_, val) in self.id_hash.iter() {
+            n += val.malloc_shallow_size_of_vec(malloc_size_of);
+        }
+
+        n += self.class_hash.malloc_shallow_size_of_hash(malloc_enclosing_size_of);
+        for (_, val) in self.class_hash.iter() {
+            n += val.malloc_shallow_size_of_vec(malloc_size_of);
+        }
+
+        n += self.local_name_hash.malloc_shallow_size_of_hash(malloc_enclosing_size_of);
+        for (_, val) in self.local_name_hash.iter() {
+            n += val.malloc_shallow_size_of_vec(malloc_size_of);
+        }
+
+        n += self.other.malloc_shallow_size_of_vec(malloc_size_of);
 
         n
     }
diff --git a/components/style/stylesheets/memory.rs b/components/style/stylesheets/memory.rs
index be77a7b5cbd..b9f4f438fe5 100644
--- a/components/style/stylesheets/memory.rs
+++ b/components/style/stylesheets/memory.rs
@@ -13,6 +13,7 @@ use hash::HashMap;
 #[cfg(feature = "gecko")]
 use servo_arc::Arc;
 use shared_lock::SharedRwLockReadGuard;
+use smallvec::{Array, SmallVec};
 use std::collections::HashSet;
 use std::hash::{BuildHasher, Hash};
 use std::os::raw::c_void;
@@ -155,6 +156,16 @@ impl<T> MallocSizeOfVec for Vec<T> {
     }
 }
 
+impl<A: Array> MallocSizeOfVec for SmallVec<A> {
+    fn malloc_shallow_size_of_vec(&self, malloc_size_of: MallocSizeOfFn) -> usize {
+        if self.spilled() {
+            unsafe { do_malloc_size_of(malloc_size_of, self.as_ptr()) }
+        } else {
+            0
+        }
+    }
+}
+
 /// Trait for measuring the heap usage of a hash table.
 pub trait MallocSizeOfHash {
     /// Measure shallowly the size of the memory used within a hash table --
diff --git a/components/style/stylist.rs b/components/style/stylist.rs
index 46747c182b9..c9211d8267c 100644
--- a/components/style/stylist.rs
+++ b/components/style/stylist.rs
@@ -1956,13 +1956,13 @@ impl CascadeData {
                                        malloc_enclosing_size_of: MallocEnclosingSizeOfFn,
                                        sizes: &mut ServoStyleSetSizes) {
         sizes.mStylistElementAndPseudosMaps +=
-            self.element_map.malloc_size_of_children(malloc_enclosing_size_of);
+            self.element_map.malloc_size_of_children(malloc_size_of, malloc_enclosing_size_of);
 
         for elem in self.pseudos_map.iter() {
             if let Some(ref elem) = *elem {
                 sizes.mStylistElementAndPseudosMaps +=
                     elem.malloc_shallow_size_of_box(malloc_size_of) +
-                    elem.malloc_size_of_children(malloc_enclosing_size_of)
+                    elem.malloc_size_of_children(malloc_size_of, malloc_enclosing_size_of)
             }
         }
 
@@ -1973,10 +1973,11 @@ impl CascadeData {
         }
 
         sizes.mStylistInvalidationMap +=
-            self.invalidation_map.malloc_size_of_children(malloc_enclosing_size_of);
+            self.invalidation_map.malloc_size_of_children(malloc_size_of, malloc_enclosing_size_of);
 
         sizes.mStylistRevalidationSelectors +=
-            self.selectors_for_cache_revalidation.malloc_size_of_children(malloc_enclosing_size_of);
+            self.selectors_for_cache_revalidation.malloc_size_of_children(malloc_size_of,
+                                                                          malloc_enclosing_size_of);
 
         sizes.mStylistOther +=
             self.effective_media_query_results.malloc_size_of_children(malloc_enclosing_size_of);