diff --git a/packages/better-auth/src/adapters/create-adapter/index.ts b/packages/better-auth/src/adapters/create-adapter/index.ts
index 1ca03d04cf..294e1f9765 100644
--- a/packages/better-auth/src/adapters/create-adapter/index.ts
+++ b/packages/better-auth/src/adapters/create-adapter/index.ts
@@ -486,6 +486,8 @@ export const createAdapter =
 			? undefined
 			: CleanedWhere[] => {
 			if (!where) return undefined as any;
+			const newMappedKeys = config.mapKeysTransformInput ?? {};
+
 			return where.map((w) => {
 				const {
 					field: unsafe_field,
@@ -504,11 +506,13 @@ export const createAdapter =
 					field: unsafe_field,
 					model,
 				});
+				const fieldName: string =
+					newMappedKeys[defaultFieldName] ||
+					getFieldName({
+						field: defaultFieldName,
+						model: defaultModelName,
+					});
 
-				const fieldName = getFieldName({
-					field: defaultFieldName,
-					model: defaultModelName,
-				});
 				const fieldAttr = getFieldAttributes({
 					field: defaultFieldName,
 					model: defaultModelName,
diff --git a/packages/better-auth/src/adapters/create-adapter/test/create-adapter.test.ts b/packages/better-auth/src/adapters/create-adapter/test/create-adapter.test.ts
index fa2857ddec..1f78dde979 100644
--- a/packages/better-auth/src/adapters/create-adapter/test/create-adapter.test.ts
+++ b/packages/better-auth/src/adapters/create-adapter/test/create-adapter.test.ts
@@ -1,6 +1,10 @@
 import { describe, test, expect } from "vitest";
 import { createAdapter } from "..";
-import type { AdapterConfig, CreateCustomAdapter } from "../types";
+import type {
+	AdapterConfig,
+	CleanedWhere,
+	CreateCustomAdapter,
+} from "../types";
 import type { BetterAuthOptions, User, Where } from "../../../types";
 import { betterAuth } from "../../../auth";
 
@@ -559,6 +563,7 @@ describe("Create Adapter Helper", async () => {
 							};
 						},
 					});
+
 					const res = (await adapter.create({
 						model: "user",
 						data: { email: "test@test.com" },
@@ -572,6 +577,33 @@ describe("Create Adapter Helper", async () => {
 				expect(parameters.data.email_address).toEqual("test@test.com");
 			});
 
+			test("Should allow custom transform input to transform the where clause", async () => {
+				const parameters: CleanedWhere[] = await new Promise(async (r) => {
+					const adapter = await createTestAdapter({
+						config: {
+							debugLogs: {},
+							mapKeysTransformInput: {
+								id: "_id",
+							},
+						},
+						adapter(args_0) {
+							return {
+								async findOne({ model, where, select }) {
+									r(where);
+									return {} as any;
+								},
+							};
+						},
+					});
+					adapter.findOne({
+						model: "user",
+						where: [{ field: "id", value: "123" }],
+					});
+				});
+
+				expect(parameters[0]!.field).toEqual("_id");
+			});
+
 			test("Should allow custom map output key transformation", async () => {
 				const parameters: {
 					data: { email: string };