diff --git a/mcp-core/src/main/java/io/modelcontextprotocol/spec/McpServerSession.java b/mcp-core/src/main/java/io/modelcontextprotocol/spec/McpServerSession.java
index 241f7d8b5..5cfdbe7e0 100644
--- a/mcp-core/src/main/java/io/modelcontextprotocol/spec/McpServerSession.java
+++ b/mcp-core/src/main/java/io/modelcontextprotocol/spec/McpServerSession.java
@@ -4,19 +4,12 @@
 
 package io.modelcontextprotocol.spec;
 
-import java.time.Duration;
-import java.util.Map;
-import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.atomic.AtomicInteger;
-import java.util.concurrent.atomic.AtomicLong;
-import java.util.concurrent.atomic.AtomicReference;
-
 import io.modelcontextprotocol.common.McpTransportContext;
+import io.modelcontextprotocol.json.TypeRef;
 import io.modelcontextprotocol.server.McpAsyncServerExchange;
 import io.modelcontextprotocol.server.McpInitRequestHandler;
 import io.modelcontextprotocol.server.McpNotificationHandler;
 import io.modelcontextprotocol.server.McpRequestHandler;
-import io.modelcontextprotocol.json.TypeRef;
 import io.modelcontextprotocol.util.Assert;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -24,6 +17,14 @@
 import reactor.core.publisher.MonoSink;
 import reactor.core.publisher.Sinks;
 
+import java.time.Duration;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.concurrent.atomic.AtomicReference;
+
 /**
  * Represents a Model Context Protocol (MCP) session on the server side. It manages
  * bidirectional JSON-RPC communication with the client.
@@ -36,7 +37,9 @@ public class McpServerSession implements McpLoggableSession {
 
 	private final String id;
 
-	/** Duration to wait for request responses before timing out */
+	/**
+	 * Duration to wait for request responses before timing out
+	 */
 	private final Duration requestTimeout;
 
 	private final AtomicLong requestCounter = new AtomicLong(0);
@@ -65,6 +68,8 @@ public class McpServerSession implements McpLoggableSession {
 
 	private volatile McpSchema.LoggingLevel minLoggingLevel = McpSchema.LoggingLevel.INFO;
 
+	private volatile AtomicBoolean closed = new AtomicBoolean(false);
+
 	/**
 	 * Creates a new server session with the given parameters and the transport to use.
 	 * @param id session id
@@ -345,14 +350,23 @@ private MethodNotFoundError getMethodNotFoundError(String method) {
 
 	@Override
 	public Mono<Void> closeGracefully() {
-		// TODO: clear pendingResponses and emit errors?
-		return this.transport.closeGracefully();
+		if (this.closed.compareAndSet(false, true)) {
+			this.pendingResponses.forEach((id, response) -> response.error(new RuntimeException("Session closed")));
+			this.pendingResponses.clear();
+			return this.transport.closeGracefully();
+		}
+		else {
+			return Mono.empty();
+		}
 	}
 
 	@Override
 	public void close() {
-		// TODO: clear pendingResponses and emit errors?
-		this.transport.close();
+		if (this.closed.compareAndSet(false, true)) {
+			this.pendingResponses.forEach((id, response) -> response.error(new RuntimeException("Session closed")));
+			this.pendingResponses.clear();
+			this.transport.close();
+		}
 	}
 
 	/**
diff --git a/mcp-spring/mcp-spring-webmvc/src/main/java/io/modelcontextprotocol/server/transport/WebMvcSseServerTransportProvider.java b/mcp-spring/mcp-spring-webmvc/src/main/java/io/modelcontextprotocol/server/transport/WebMvcSseServerTransportProvider.java
index 6c35de56d..807ccc0fe 100644
--- a/mcp-spring/mcp-spring-webmvc/src/main/java/io/modelcontextprotocol/server/transport/WebMvcSseServerTransportProvider.java
+++ b/mcp-spring/mcp-spring-webmvc/src/main/java/io/modelcontextprotocol/server/transport/WebMvcSseServerTransportProvider.java
@@ -263,10 +263,13 @@ private ServerResponse handleSseConnection(ServerRequest request) {
 			logger.debug("Creating new SSE connection for session: {}", sessionId);
 			sseBuilder.onComplete(() -> {
 				logger.debug("SSE connection completed for session: {}", sessionId);
+				// explicitly close the session when the SSE connection is completed
+				session.close();
 				sessions.remove(sessionId);
 			});
 			sseBuilder.onTimeout(() -> {
 				logger.debug("SSE connection timed out for session: {}", sessionId);
+				session.close();
 				sessions.remove(sessionId);
 			});
 			this.sessions.put(sessionId, session);
@@ -383,6 +386,12 @@ public Mono<Void> sendMessage(McpSchema.JSONRPCMessage message) {
 					String jsonText = jsonMapper.writeValueAsString(message);
 					sseBuilder.event(MESSAGE_EVENT_TYPE).data(jsonText);
 				}
+				catch (IOException e) {
+					if (logger.isDebugEnabled()) {
+						logger.debug("Failed to send message: {}", e.getMessage());
+					}
+					sseBuilder.error(e);
+				}
 				catch (Exception e) {
 					logger.error("Failed to send message: {}", e.getMessage());
 					sseBuilder.error(e);