diff --git a/packages/next-safe-action/src/action-builder.ts b/packages/next-safe-action/src/action-builder.ts
index df4881d..fc55bbd 100644
--- a/packages/next-safe-action/src/action-builder.ts
+++ b/packages/next-safe-action/src/action-builder.ts
@@ -21,7 +21,6 @@ import {
 	isRedirectError,
 	winningBoolean,
 } from "./utils";
-import type { MaybePromise } from "./utils.types";
 import {
 	ActionMetadataValidationError,
 	ActionOutputDataValidationError,
@@ -295,11 +294,11 @@ export function actionBuilder<
 					// Execute middleware chain + action function.
 					await executeMiddlewareStack();
 
-					const callbacksToExecute: MaybePromise<unknown>[] = [];
+					const callbackPromises: (Promise<unknown> | undefined)[] = [];
 
 					// If an internal framework error occurred, throw it, so it will be processed by Next.js.
 					if (frameworkError) {
-						callbacksToExecute.push(
+						callbackPromises.push(
 							utils?.onSuccess?.({
 								data: undefined,
 								metadata: args.metadata,
@@ -314,7 +313,7 @@ export function actionBuilder<
 							})
 						);
 
-						callbacksToExecute.push(
+						callbackPromises.push(
 							utils?.onSettled?.({
 								metadata: args.metadata,
 								ctx: currentCtx as Ctx,
@@ -327,7 +326,7 @@ export function actionBuilder<
 							})
 						);
 
-						await Promise.all(callbacksToExecute);
+						await Promise.all(callbackPromises);
 
 						throw frameworkError;
 					}
@@ -361,7 +360,7 @@ export function actionBuilder<
 							actionResult.data = middlewareResult.data as Data;
 						}
 
-						callbacksToExecute.push(
+						callbackPromises.push(
 							utils?.onSuccess?.({
 								metadata: args.metadata,
 								ctx: currentCtx as Ctx,
@@ -376,7 +375,7 @@ export function actionBuilder<
 							})
 						);
 					} else {
-						callbacksToExecute.push(
+						callbackPromises.push(
 							utils?.onError?.({
 								metadata: args.metadata,
 								ctx: currentCtx as Ctx,
@@ -388,7 +387,7 @@ export function actionBuilder<
 					}
 
 					// onSettled, if provided, is always executed.
-					callbacksToExecute.push(
+					callbackPromises.push(
 						utils?.onSettled?.({
 							metadata: args.metadata,
 							ctx: currentCtx as Ctx,
@@ -401,7 +400,7 @@ export function actionBuilder<
 						})
 					);
 
-					await Promise.all(callbacksToExecute);
+					await Promise.all(callbackPromises);
 
 					return actionResult;
 				};
diff --git a/packages/next-safe-action/src/index.ts b/packages/next-safe-action/src/index.ts
index bfd181b..0ff1a1a 100644
--- a/packages/next-safe-action/src/index.ts
+++ b/packages/next-safe-action/src/index.ts
@@ -60,11 +60,13 @@ export const createSafeActionClient = <
 		metadata: undefined as MetadataSchema extends Schema ? Infer<MetadataSchema> : undefined,
 		defaultValidationErrorsShape: (createOpts?.defaultValidationErrorsShape ?? "formatted") as ODVES,
 		throwValidationErrors: Boolean(createOpts?.throwValidationErrors),
-		handleValidationErrorsShape:
-			createOpts?.defaultValidationErrorsShape === "flattened" ? flattenValidationErrors : formatValidationErrors,
-		handleBindArgsValidationErrorsShape:
+		handleValidationErrorsShape: async (ve) =>
 			createOpts?.defaultValidationErrorsShape === "flattened"
-				? flattenBindArgsValidationErrors
-				: formatBindArgsValidationErrors,
+				? flattenValidationErrors(ve)
+				: formatValidationErrors(ve),
+		handleBindArgsValidationErrorsShape: async (ve) =>
+			createOpts?.defaultValidationErrorsShape === "flattened"
+				? flattenBindArgsValidationErrors(ve)
+				: formatBindArgsValidationErrors(ve),
 	});
 };
diff --git a/packages/next-safe-action/src/index.types.ts b/packages/next-safe-action/src/index.types.ts
index 2c14927..99d8eda 100644
--- a/packages/next-safe-action/src/index.types.ts
+++ b/packages/next-safe-action/src/index.types.ts
@@ -176,14 +176,14 @@ export type SafeActionUtils<
 		hasRedirected: boolean;
 		hasNotFound: boolean;
 		hasForbidden: boolean;
-	}) => MaybePromise<unknown>;
+	}) => Promise<unknown>;
 	onError?: (args: {
 		error: Prettify<Omit<SafeActionResult<ServerError, S, BAS, CVE, CBAVE, Data>, "data">>;
 		metadata: MD;
 		ctx?: Prettify<Ctx>;
 		clientInput: S extends Schema ? InferIn<S> : undefined;
 		bindArgsClientInputs: InferInArray<BAS>;
-	}) => MaybePromise<unknown>;
+	}) => Promise<unknown>;
 	onSettled?: (args: {
 		result: Prettify<SafeActionResult<ServerError, S, BAS, CVE, CBAVE, Data>>;
 		metadata: MD;
@@ -193,7 +193,7 @@ export type SafeActionUtils<
 		hasRedirected: boolean;
 		hasNotFound: boolean;
 		hasForbidden: boolean;
-	}) => MaybePromise<unknown>;
+	}) => Promise<unknown>;
 };
 
 /**
diff --git a/packages/next-safe-action/src/validation-errors.types.ts b/packages/next-safe-action/src/validation-errors.types.ts
index 06c7505..5463c0b 100644
--- a/packages/next-safe-action/src/validation-errors.types.ts
+++ b/packages/next-safe-action/src/validation-errors.types.ts
@@ -63,7 +63,7 @@ export type HandleValidationErrorsShapeFn<
 		metadata: MD;
 		ctx: Prettify<Ctx>;
 	}
-) => CVE | Promise<CVE>;
+) => Promise<CVE>;
 
 /**
  * Type of the function used to format bind arguments validation errors.
@@ -82,4 +82,4 @@ export type HandleBindArgsValidationErrorsShapeFn<
 		metadata: MD;
 		ctx: Prettify<Ctx>;
 	}
-) => CBAVE | Promise<CBAVE>;
+) => Promise<CBAVE>;