diff --git a/src/shared/protocol.test.ts b/src/shared/protocol.test.ts
index e0141da19..05bc8f3bc 100644
--- a/src/shared/protocol.test.ts
+++ b/src/shared/protocol.test.ts
@@ -27,9 +27,11 @@ class MockTransport implements Transport {
 describe("protocol tests", () => {
   let protocol: Protocol<Request, Notification, Result>;
   let transport: MockTransport;
+  let sendSpy: jest.SpyInstance;
 
   beforeEach(() => {
     transport = new MockTransport();
+    sendSpy = jest.spyOn(transport, 'send');
     protocol = new (class extends Protocol<Request, Notification, Result> {
       protected assertCapabilityForMethod(): void {}
       protected assertNotificationCapability(): void {}
@@ -63,6 +65,130 @@ describe("protocol tests", () => {
     expect(oncloseMock).toHaveBeenCalled();
   });
 
+  describe("_meta preservation with onprogress", () => {
+    test("should preserve existing _meta when adding progressToken", async () => {
+      await protocol.connect(transport);
+      const request = { 
+        method: "example", 
+        params: {
+          data: "test",
+          _meta: {
+            customField: "customValue",
+            anotherField: 123
+          }
+        }
+      };
+      const mockSchema: ZodType<{ result: string }> = z.object({
+        result: z.string(),
+      });
+      const onProgressMock = jest.fn();
+      
+      protocol.request(request, mockSchema, {
+        onprogress: onProgressMock,
+      });
+      
+      expect(sendSpy).toHaveBeenCalledWith(expect.objectContaining({
+        method: "example",
+        params: {
+          data: "test",
+          _meta: {
+            customField: "customValue",
+            anotherField: 123,
+            progressToken: expect.any(Number)
+          }
+        },
+        jsonrpc: "2.0",
+        id: expect.any(Number)
+      }), expect.any(Object));
+    });
+
+    test("should create _meta with progressToken when no _meta exists", async () => {
+      await protocol.connect(transport);
+      const request = { 
+        method: "example", 
+        params: {
+          data: "test"
+        }
+      };
+      const mockSchema: ZodType<{ result: string }> = z.object({
+        result: z.string(),
+      });
+      const onProgressMock = jest.fn();
+      
+      protocol.request(request, mockSchema, {
+        onprogress: onProgressMock,
+      });
+      
+      expect(sendSpy).toHaveBeenCalledWith(expect.objectContaining({
+        method: "example",
+        params: {
+          data: "test",
+          _meta: {
+            progressToken: expect.any(Number)
+          }
+        },
+        jsonrpc: "2.0",
+        id: expect.any(Number)
+      }), expect.any(Object));
+    });
+
+    test("should not modify _meta when onprogress is not provided", async () => {
+      await protocol.connect(transport);
+      const request = { 
+        method: "example", 
+        params: {
+          data: "test",
+          _meta: {
+            customField: "customValue"
+          }
+        }
+      };
+      const mockSchema: ZodType<{ result: string }> = z.object({
+        result: z.string(),
+      });
+      
+      protocol.request(request, mockSchema);
+      
+      expect(sendSpy).toHaveBeenCalledWith(expect.objectContaining({
+        method: "example",
+        params: {
+          data: "test",
+          _meta: {
+            customField: "customValue"
+          }
+        },
+        jsonrpc: "2.0",
+        id: expect.any(Number)
+      }), expect.any(Object));
+    });
+
+    test("should handle params being undefined with onprogress", async () => {
+      await protocol.connect(transport);
+      const request = { 
+        method: "example"
+      };
+      const mockSchema: ZodType<{ result: string }> = z.object({
+        result: z.string(),
+      });
+      const onProgressMock = jest.fn();
+      
+      protocol.request(request, mockSchema, {
+        onprogress: onProgressMock,
+      });
+      
+      expect(sendSpy).toHaveBeenCalledWith(expect.objectContaining({
+        method: "example",
+        params: {
+          _meta: {
+            progressToken: expect.any(Number)
+          }
+        },
+        jsonrpc: "2.0",
+        id: expect.any(Number)
+      }), expect.any(Object));
+    });
+  });
+
   describe("progress notification timeout behavior", () => {
     beforeEach(() => {
       jest.useFakeTimers();
diff --git a/src/shared/protocol.ts b/src/shared/protocol.ts
index 4694929d7..a04f26eb2 100644
--- a/src/shared/protocol.ts
+++ b/src/shared/protocol.ts
@@ -541,7 +541,10 @@ export abstract class Protocol<
         this._progressHandlers.set(messageId, options.onprogress);
         jsonrpcRequest.params = {
           ...request.params,
-          _meta: { progressToken: messageId },
+          _meta: {
+            ...(request.params?._meta || {}),
+            progressToken: messageId
+          },
         };
       }