diff --git a/src/builtin/color/hsl.rs b/src/builtin/color/hsl.rs
index 3501875..8575890 100644
--- a/src/builtin/color/hsl.rs
+++ b/src/builtin/color/hsl.rs
@@ -100,7 +100,7 @@ pub(crate) fn register(f: &mut BTreeMap<String, Builtin>) {
             v => return Err(format!("$color: {} is not a color.", v).into()),
         };
         let amount = match arg!(args, 1, "amount").eval() {
-            Value::Dimension(n, _) => n / Number::from(100),
+            Value::Dimension(n, u) => bound!("amount", n, u, 0, 100) / Number::from(100),
             v => return Err(format!("$amount: {} is not a number.", v).into())
         };
         Ok(Value::Color(color.darken(amount)))
@@ -112,7 +112,7 @@ pub(crate) fn register(f: &mut BTreeMap<String, Builtin>) {
             v => return Err(format!("$color: {} is not a color.", v).into()),
         };
         let amount = match arg!(args, 1, "amount").eval() {
-            Value::Dimension(n, _) => n / Number::from(100),
+            Value::Dimension(n, u) => bound!("amount", n, u, 0, 100) / Number::from(100),
             v => return Err(format!("$amount: {} is not a number.", v).into())
         };
         Ok(Value::Color(color.saturate(amount)))
@@ -124,7 +124,7 @@ pub(crate) fn register(f: &mut BTreeMap<String, Builtin>) {
             v => return Err(format!("$color: {} is not a color.", v).into()),
         };
         let amount = match arg!(args, 1, "amount").eval() {
-            Value::Dimension(n, _) => n / Number::from(100),
+            Value::Dimension(n, u) => bound!("amount", n, u, 0, 100) / Number::from(100),
             v => return Err(format!("$amount: {} is not a number.", v).into())
         };
         Ok(Value::Color(color.desaturate(amount)))