diff --git a/src/Numeric/MathExpr.hs b/src/Numeric/MathExpr.hs
index 7db9765..ee80a32 100644
--- a/src/Numeric/MathExpr.hs
+++ b/src/Numeric/MathExpr.hs
@@ -73,7 +73,7 @@ module Numeric.MathExpr
         where
           replace c
             | isVariable c = pad $ show $ fromJust $ c `lookup` vars
-            | otherwise = c
+            | otherwise = pad c
 
           isVariable c = isJust $ c `lookup` vars