diff --git a/components/style/values/generics/grid.rs b/components/style/values/generics/grid.rs
index d7e817762c3..8093fdfea7a 100644
--- a/components/style/values/generics/grid.rs
+++ b/components/style/values/generics/grid.rs
@@ -58,6 +58,7 @@ impl ToCss for GridLine {
         }
 
         if let Some(i) = self.line_num {
+            dest.write_str(" ")?;
             i.value().to_css(dest)?;
         }