diff --git a/main.fs b/main.fs
index 271bef4..5ea3622 100644
--- a/main.fs
+++ b/main.fs
@@ -127,7 +127,7 @@ S" you feel like throwing some stuff into the pool." set-message
 : can-afford? ( n currency -- flag ) f@ s>f f>= ;
 
 \ the word pay pays an amount of a currency.
-: pay ( n currency -- ) dup f@ swap s>f fswap f- f! ;
+: pay ( n currency -- ) dup f@ swap s>f ( fswap ) f- f! ;
 
 \ the word clear-message clears the onscreen message
 : clear-message S"  " set-message ;