diff --git a/src/cli/cli.rs b/src/cli/cli.rs
index 5a0daa2..9cfd4eb 100644
--- a/src/cli/cli.rs
+++ b/src/cli/cli.rs
@@ -72,7 +72,7 @@ pub(super) struct PlayOpts {
     /// Add a slope expression named NAME which mutates the VARIABLE with the result of EXPR each frame
     #[arg(short, long = "slope", value_name = "NAME:VARIABLE=EXPR", value_parser = parse_key_tuple::<LetterString, Letter, Expression>)]
     #[getset(skip)]
-    slopes: Vec<(LetterString, (char, Expression))>,
+    slopes: Vec<(LetterString, (Letter, Expression))>,
 }
 
 impl PlayOpts {
@@ -87,7 +87,7 @@ impl PlayOpts {
     pub(super) fn slopes(&self) -> impl Iterator<Item = (&String, (&char, &Expression))> {
         self.slopes
             .iter()
-            .map(|(name, (v, e))| (name.as_ref(), (v, e)))
+            .map(|(name, (v, e))| (name.as_ref(), (v.as_ref(), e)))
     }
 }