diff --git a/src/sumtype.ts b/src/sumtype.ts
index 144c677..0527a2f 100644
--- a/src/sumtype.ts
+++ b/src/sumtype.ts
@@ -34,7 +34,7 @@ abstract class SumType<M extends Variants> implements Setoid, Show {
     } else if (pattern._) {
       return pattern._();
     } else {
-      throw `caseOf pattern is missing a function for ${this.kind}`;
+      throw new Error(`caseOf pattern is missing a function for ${this.kind}`);
     }
   }