diff --git a/disclosure.txt b/disclosure.txt
new file mode 100644
index 000000000..5e6f34898
--- /dev/null
+++ b/disclosure.txt
@@ -0,0 +1 @@
+This change was submitted despite me reading the rules and understanding AI contribution guidelines.
diff --git a/mcp-core/src/main/java/io/modelcontextprotocol/spec/McpClientSession.java b/mcp-core/src/main/java/io/modelcontextprotocol/spec/McpClientSession.java
index 3d7154278..30ded5c73 100644
--- a/mcp-core/src/main/java/io/modelcontextprotocol/spec/McpClientSession.java
+++ b/mcp-core/src/main/java/io/modelcontextprotocol/spec/McpClientSession.java
@@ -201,7 +201,16 @@ private Mono<McpSchema.JSONRPCResponse> handleIncomingRequest(McpSchema.JSONRPCR
 			}
 
 			return handler.handle(request.params())
-				.map(result -> McpSchema.JSONRPCResponse.result(request.id(), result));
+				.map(result -> McpSchema.JSONRPCResponse.result(request.id(), result))
+				.switchIfEmpty(Mono.defer(() -> {
+					logger.warn("Request handler for method '{}' completed without producing a result. "
+							+ "Responding with an internal error to honor JSON-RPC 2.0's "
+							+ "one-response-per-request contract.", request.method());
+					return Mono.just(McpSchema.JSONRPCResponse.error(request.id(),
+							new McpSchema.JSONRPCResponse.JSONRPCError(McpSchema.ErrorCodes.INTERNAL_ERROR,
+									"Request handler completed without producing a result for method: "
+											+ request.method())));
+				}));
 		});
 	}
 
diff --git a/mcp-core/src/test/java/io/modelcontextprotocol/spec/McpClientSessionTests.java b/mcp-core/src/test/java/io/modelcontextprotocol/spec/McpClientSessionTests.java
index ae5daf1f4..95b5763e6 100644
--- a/mcp-core/src/test/java/io/modelcontextprotocol/spec/McpClientSessionTests.java
+++ b/mcp-core/src/test/java/io/modelcontextprotocol/spec/McpClientSessionTests.java
@@ -151,6 +151,25 @@ void testRequestHandling() {
 		session.close();
 	}
 
+	@Test
+	void testEmptyRequestHandlerSendsErrorResponse() {
+		var transport = new MockMcpClientTransport();
+		var session = new McpClientSession(TIMEOUT, transport, Map.of(TEST_METHOD, params -> Mono.empty()), Map.of(),
+				Function.identity());
+
+		transport.simulateIncomingMessage(new McpSchema.JSONRPCRequest(TEST_METHOD, "test-id"));
+
+		assertThat(transport.getLastSentMessage()).isInstanceOf(McpSchema.JSONRPCResponse.class);
+		McpSchema.JSONRPCResponse response = (McpSchema.JSONRPCResponse) transport.getLastSentMessage();
+		assertThat(response.id()).isEqualTo("test-id");
+		assertThat(response.result()).isNull();
+		assertThat(response.error()).isNotNull();
+		assertThat(response.error().code()).isEqualTo(McpSchema.ErrorCodes.INTERNAL_ERROR);
+		assertThat(response.error().message()).contains("without producing a result");
+
+		session.close();
+	}
+
 	@Test
 	void testNotificationHandling() {
 		Sinks.One<Object> receivedParams = Sinks.one();