diff --git a/src/servo/layout/box.rs b/src/servo/layout/box.rs
index e92b6813134..73087d74383 100644
--- a/src/servo/layout/box.rs
+++ b/src/servo/layout/box.rs
@@ -101,6 +101,7 @@ trait RenderBoxMethods {
 
     pure fn is_replaced() -> bool;
     pure fn can_split() -> bool;
+    pure fn is_whitespace_only() -> bool;
     pure fn can_merge_with_box(@self, other: @RenderBox) -> bool;
     pure fn requires_inline_spacers() -> bool;
     pure fn content_box() -> Rect<au>;
@@ -149,6 +150,13 @@ impl RenderBox : RenderBoxMethods {
         }
     }
 
+    pure fn is_whitespace_only() -> bool {
+        match self {
+            UnscannedTextBox(_, raw_text) => raw_text.is_whitespace(),
+            _ => false
+        }
+    }
+
     pure fn can_merge_with_box(@self, other: @RenderBox) -> bool {
         assert !core::box::ptr_eq(self, other);