diff --git a/components/layout/lib.rs b/components/layout/lib.rs
index 9f943cf48b3..b272ad503de 100644
--- a/components/layout/lib.rs
+++ b/components/layout/lib.rs
@@ -98,3 +98,4 @@ pub mod wrapper;
 
 // For unit tests:
 pub use fragment::Fragment;
+pub use fragment::SpecificFragmentInfo;
diff --git a/tests/unit/layout/size_of.rs b/tests/unit/layout/size_of.rs
index 320f85e0169..08d11df86cd 100644
--- a/tests/unit/layout/size_of.rs
+++ b/tests/unit/layout/size_of.rs
@@ -3,24 +3,35 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use layout::Fragment;
+use layout::SpecificFragmentInfo;
 use std::mem::size_of;
 
+fn check_size_for(name: &'static str, expected: usize, actual: usize) {
+    if actual < expected {
+        panic!("Your changes have decreased the stack size of {} \
+                from {} to {}. Good work! Please update the size in tests/unit/layout/size_of.rs",
+                name, expected, actual);
+    }
+
+    if actual > expected {
+        panic!("Your changes have increased the stack size of {} \
+                from {} to {}.  Please consider choosing a design which avoids this increase. \
+                If you feel that the increase is necessary, update the size in \
+                tests/unit/layout/size_of.rs.",
+                name, expected, actual);
+    }
+}
+
 #[test]
 fn test_size_of_fragment() {
     let expected = 160;
     let actual = size_of::<Fragment>();
-
-    if actual < expected {
-        panic!("Your changes have decreased the stack size of layout::fragment::Fragment \
-                from {} to {}. Good work! Please update the size in tests/unit/layout/size_of.rs",
-                expected, actual);
-    }
-
-    if actual > expected {
-        panic!("Your changes have increased the stack size of layout::fragment::Fragment \
-                from {} to {}.  Please consider choosing a design which avoids this increase. \
-                If you feel that the increase is necessary, update the size in \
-                tests/unit/layout/size_of.rs.",
-                expected, actual);
-    }
+    check_size_for("layout::fragment::Fragment", expected, actual);
+}
+
+#[test]
+fn test_size_of_specific_fragment_info() {
+    let expected = 24;
+    let actual = size_of::<SpecificFragmentInfo>();
+    check_size_for("layout::fragment::SpecificFragmentInfo", expected, actual);
 }