diff --git a/src/errors/index.ts b/src/errors/index.ts
new file mode 100644
index 0000000..cc1f5da
--- /dev/null
+++ b/src/errors/index.ts
@@ -0,0 +1 @@
+export { UnsupportedAlgorithmError } from './unsupported-algorithm-error';
diff --git a/src/errors/unsupported-algorithm-error.ts b/src/errors/unsupported-algorithm-error.ts
new file mode 100644
index 0000000..b770515
--- /dev/null
+++ b/src/errors/unsupported-algorithm-error.ts
@@ -0,0 +1,6 @@
+/**
+ * Thrown when a key is presented to verify a signature with
+ * an algorithm that is not supported
+ */
+export class UnsupportedAlgorithmError extends Error {
+}
diff --git a/src/httpbis/index.ts b/src/httpbis/index.ts
index b5664cd..3586b16 100644
--- a/src/httpbis/index.ts
+++ b/src/httpbis/index.ts
@@ -24,6 +24,7 @@ import {
     CommonConfig,
     VerifyingKey,
 } from '../types';
+import { UnsupportedAlgorithmError } from '../errors';
 
 export function deriveComponent(component: string, params: Map<string, string | number | boolean>, res: Response, req?: Request): string[];
 export function deriveComponent(component: string, params: Map<string, string | number | boolean>, req: Request): string[];
@@ -378,6 +379,10 @@ export async function verifyMessage(config: VerifyConfig, message: Request | Res
                 return params;
             }, {})),
         ]);
+        if (input[1].has('alg') && key.algs?.includes(input[1].get('alg') as string) === false) {
+            throw new UnsupportedAlgorithmError('Unsupported key algorithm');
+        }
+        // @todo - confirm this is all working as expected
         if (!config.all && !key) {
             return null;
         }