diff --git a/core/src/shapes.rs b/core/src/shapes.rs
index 0cedc7c..9edbbb5 100644
--- a/core/src/shapes.rs
+++ b/core/src/shapes.rs
@@ -70,7 +70,7 @@ impl Shape {
     }
 
     #[must_use]
-    pub fn is_promotable(&self) -> bool {
+    pub const fn is_promotable(&self) -> bool {
         matches!(self, Self::Knight | Self::Bishop | Self::Rook | Self::Queen)
     }