diff --git a/frameworks/blueprint/stylesheets/blueprint/modules/_grid.sass b/frameworks/blueprint/stylesheets/blueprint/modules/_grid.sass
index 3d0680e939..419d60819c 100644
--- a/frameworks/blueprint/stylesheets/blueprint/modules/_grid.sass
+++ b/frameworks/blueprint/stylesheets/blueprint/modules/_grid.sass
@@ -146,8 +146,8 @@
 
 // Border with more whitespace, spans one column.
 =colborder
-  :padding-right= !blueprint_grid_width - 0.5 * !blueprint_grid_margin - 1
-  :margin-right= !blueprint_grid_width - 0.5 * !blueprint_grid_margin
+  :padding-right= (!blueprint_grid_width - 2 * !blueprint_grid_margin - 1)/2
+  :margin-right= (!blueprint_grid_width - 2 * !blueprint_grid_margin)/2
   :border-right 1px solid #eee
 
 // Mixin this to an hr to make a horizontal ruler across a column.
diff --git a/frameworks/blueprint/stylesheets/blueprint/modules/_rtl.sass b/frameworks/blueprint/stylesheets/blueprint/modules/_rtl.sass
index 27301e28e4..1efaa2dc26 100644
--- a/frameworks/blueprint/stylesheets/blueprint/modules/_rtl.sass
+++ b/frameworks/blueprint/stylesheets/blueprint/modules/_rtl.sass
@@ -66,8 +66,8 @@
 
 // Border with more whitespace, spans one column.
 =colborder
-  :padding-left= !blueprint_grid_width - 0.5 * !blueprint_grid_margin - 1
-  :margin-left= !blueprint_grid_width - 0.5 * !blueprint_grid_margin
+  :padding-left= (!blueprint_grid_width - 2 * !blueprint_grid_margin - 1)/2
+  :margin-left= (!blueprint_grid_width - 2 * !blueprint_grid_margin)/2
   :border-left 1px solid #eee
 
 =rtl-typography(!body_selector = "body")