diff --git a/packages/middleware-signing/src/middleware.ts b/packages/middleware-signing/src/middleware.ts
index dc3b4bcc06b2..a8905f9e6771 100644
--- a/packages/middleware-signing/src/middleware.ts
+++ b/packages/middleware-signing/src/middleware.ts
@@ -24,8 +24,9 @@ export const awsAuthMiddleware =
 
       // TODO(identityandauth): call authScheme resolver
       const authScheme: AuthScheme | undefined = context.endpointV2?.properties?.authSchemes?.[0];
+
       const multiRegionOverride: string | undefined =
-        authScheme?.name === "sigv4a" ? authScheme?.signingRegionSet?.[0] : undefined;
+        authScheme?.name === "sigv4a" ? authScheme?.signingRegionSet?.join(",") : undefined;
 
       const signer = await options.signer(authScheme);
 
diff --git a/packages/types/src/auth.ts b/packages/types/src/auth.ts
index 0d8964b6702a..01fb55ac75d8 100644
--- a/packages/types/src/auth.ts
+++ b/packages/types/src/auth.ts
@@ -15,7 +15,8 @@ export interface AuthScheme {
    */
   signingRegion: string;
   /**
-   * TODO usage?
+   * @example ["*"]
+   * @exammple ["us-west-2", "us-east-1"]
    */
   signingRegionSet?: string[];
   /**