diff --git a/mcp/src/main/java/io/modelcontextprotocol/spec/McpClientSession.java b/mcp/src/main/java/io/modelcontextprotocol/spec/McpClientSession.java
index f577b493..ff59d8bc 100644
--- a/mcp/src/main/java/io/modelcontextprotocol/spec/McpClientSession.java
+++ b/mcp/src/main/java/io/modelcontextprotocol/spec/McpClientSession.java
@@ -242,6 +242,11 @@ public <T> Mono<T> sendRequest(String method, Object requestParams, TypeReferenc
 					this.pendingResponses.remove(requestId);
 					sink.error(error);
 				});
+			sink.onDispose(() -> {
+				if (this.pendingResponses.remove(requestId) != null) {
+					logger.debug("Request {} disposed (e.g., timeout, cancellation), removed from client pendingResponses.", requestId);
+				}
+			});
 		})).timeout(this.requestTimeout).handle((jsonRpcResponse, sink) -> {
 			if (jsonRpcResponse.error() != null) {
 				logger.error("Error handling request: {}", jsonRpcResponse.error());
diff --git a/mcp/src/main/java/io/modelcontextprotocol/spec/McpServerSession.java b/mcp/src/main/java/io/modelcontextprotocol/spec/McpServerSession.java
index 86906d85..f7f7fab7 100644
--- a/mcp/src/main/java/io/modelcontextprotocol/spec/McpServerSession.java
+++ b/mcp/src/main/java/io/modelcontextprotocol/spec/McpServerSession.java
@@ -121,6 +121,11 @@ public <T> Mono<T> sendRequest(String method, Object requestParams, TypeReferenc
 				this.pendingResponses.remove(requestId);
 				sink.error(error);
 			});
+			sink.onDispose(() -> {
+				if (this.pendingResponses.remove(requestId) != null) {
+					logger.debug("Request {} disposed (e.g., timeout, cancellation), removed from client pendingResponses.", requestId);
+				}
+			});
 		}).timeout(requestTimeout).handle((jsonRpcResponse, sink) -> {
 			if (jsonRpcResponse.error() != null) {
 				sink.error(new McpError(jsonRpcResponse.error()));