diff --git a/doc/cli-design.txt b/doc/cli-design.txt
index 5bf59b0..15e0016 100644
--- a/doc/cli-design.txt
+++ b/doc/cli-design.txt
@@ -14,7 +14,7 @@ options:
         -n NOTE[,...], --notes NOTE[,...]
             available notes: a list of comma-separated alphabetical note names
         -e EXPR, --expression EXPR
-            signal expression (instrument) to generate music samples (you can use the floating-point number t for the current time in seconds, n for the indice of the currently playing note in the list of available notes starting with 0 and N for the number of available notes)  [default: sin(2*PI*n*(442+442*((n+1)/N))*t)]
+            signal expression (instrument) to generate music samples (you can use the floating-point number t for the current time in seconds, n for the indice of the currently playing note in the list of available notes starting with 0 and N for the number of available notes)  [default: sin(2*PI*(442+442*((n+1)/N))*t)]
 
     exporting music:
         -E, --export