diff --git a/packages/middleware-flexible-checksums/src/resolveFlexibleChecksumsConfig.spec.ts b/packages/middleware-flexible-checksums/src/resolveFlexibleChecksumsConfig.spec.ts
index 7bb1cd64f0d68..59d909a607f39 100644
--- a/packages/middleware-flexible-checksums/src/resolveFlexibleChecksumsConfig.spec.ts
+++ b/packages/middleware-flexible-checksums/src/resolveFlexibleChecksumsConfig.spec.ts
@@ -1,6 +1,11 @@
 import { normalizeProvider } from "@smithy/util-middleware";
 
-import { DEFAULT_REQUEST_CHECKSUM_CALCULATION, DEFAULT_RESPONSE_CHECKSUM_VALIDATION } from "./constants";
+import {
+  DEFAULT_REQUEST_CHECKSUM_CALCULATION,
+  DEFAULT_RESPONSE_CHECKSUM_VALIDATION,
+  RequestChecksumCalculation,
+  ResponseChecksumValidation,
+} from "./constants";
 import { resolveFlexibleChecksumsConfig } from "./resolveFlexibleChecksumsConfig";
 
 jest.mock("@smithy/util-middleware");
@@ -25,8 +30,8 @@ describe(resolveFlexibleChecksumsConfig.name, () => {
 
   it("normalizes client checksums configuration", () => {
     const mockInput = {
-      requestChecksumCalculation: "WHEN_REQUIRED",
-      responseChecksumValidation: "WHEN_REQUIRED",
+      requestChecksumCalculation: RequestChecksumCalculation.WHEN_REQUIRED,
+      responseChecksumValidation: ResponseChecksumValidation.WHEN_REQUIRED,
     };
     const resolvedConfig = resolveFlexibleChecksumsConfig(mockInput);
     expect(resolvedConfig).toEqual(mockInput);
diff --git a/packages/middleware-flexible-checksums/src/resolveFlexibleChecksumsConfig.ts b/packages/middleware-flexible-checksums/src/resolveFlexibleChecksumsConfig.ts
index b57f894b23fbd..57cfd22e7ed91 100644
--- a/packages/middleware-flexible-checksums/src/resolveFlexibleChecksumsConfig.ts
+++ b/packages/middleware-flexible-checksums/src/resolveFlexibleChecksumsConfig.ts
@@ -1,23 +1,28 @@
 import { Provider } from "@smithy/types";
 import { normalizeProvider } from "@smithy/util-middleware";
 
-import { DEFAULT_REQUEST_CHECKSUM_CALCULATION, DEFAULT_RESPONSE_CHECKSUM_VALIDATION } from "./constants";
+import {
+  DEFAULT_REQUEST_CHECKSUM_CALCULATION,
+  DEFAULT_RESPONSE_CHECKSUM_VALIDATION,
+  RequestChecksumCalculation,
+  ResponseChecksumValidation,
+} from "./constants";
 
 export interface FlexibleChecksumsInputConfig {
   /**
    * Determines when a checksum will be calculated for request payloads.
    */
-  requestChecksumCalculation?: string | Provider<string>;
+  requestChecksumCalculation?: RequestChecksumCalculation | Provider<RequestChecksumCalculation>;
 
   /**
    * Determines when checksum validation will be performed on response payloads.
    */
-  responseChecksumValidation?: string | Provider<string>;
+  responseChecksumValidation?: ResponseChecksumValidation | Provider<ResponseChecksumValidation>;
 }
 
 export interface FlexibleChecksumsResolvedConfig {
-  requestChecksumCalculation: Provider<string>;
-  responseChecksumValidation: Provider<string>;
+  requestChecksumCalculation: Provider<RequestChecksumCalculation>;
+  responseChecksumValidation: Provider<ResponseChecksumValidation>;
 }
 
 export const resolveFlexibleChecksumsConfig = <T>(