diff --git a/src/Transport/JsonRpc/ProcessJsonRpcClient.php b/src/Transport/JsonRpc/ProcessJsonRpcClient.php
index 2be07f3..26e5188 100644
--- a/src/Transport/JsonRpc/ProcessJsonRpcClient.php
+++ b/src/Transport/JsonRpc/ProcessJsonRpcClient.php
@@ -124,11 +124,13 @@ private function waitForResponse(int|string $requestId, ?float $deadline): array
     private function readProcessOutput(): void
     {
         $stdout = $this->process->getIncrementalOutput();
+        $this->process->clearOutput();
         if ('' !== $stdout) {
             $this->outputBuffer .= $stdout;
         }
 
         $stderr = $this->process->getIncrementalErrorOutput();
+        $this->process->clearErrorOutput();
         if ('' !== $stderr) {
             $this->logger->warning('Process stderr', ['stderr' => $stderr]);
         }
diff --git a/tests/Unit/Transport/JsonRpc/ProcessJsonRpcClientTest.php b/tests/Unit/Transport/JsonRpc/ProcessJsonRpcClientTest.php
index 4ab1016..d1378b4 100644
--- a/tests/Unit/Transport/JsonRpc/ProcessJsonRpcClientTest.php
+++ b/tests/Unit/Transport/JsonRpc/ProcessJsonRpcClientTest.php
@@ -144,4 +144,56 @@ public function testInputStreamWriteFailureThrowsNetworkException(): void
 
         $client->send('test.method');
     }
+
+    public function testReadProcessOutputClearsBothProcessBuffers(): void
+    {
+        $mockProcess = $this->createMock(Process::class);
+        $mockProcessLauncher = $this->createMock(ProcessLauncherInterface::class);
+
+        $mockProcess->method('isRunning')->willReturn(true);
+        $mockProcess->method('getPid')->willReturn(12345);
+        $mockProcess->method('getIncrementalOutput')->willReturn('');
+        $mockProcess->method('getIncrementalErrorOutput')->willReturn('');
+        $mockProcess->expects($this->once())->method('clearOutput');
+        $mockProcess->expects($this->once())->method('clearErrorOutput');
+        $mockProcessLauncher->method('getInputStream')->willReturn($this->mockInputStream);
+        $mockProcessLauncher->method('ensureRunning');
+
+        $client = new ProcessJsonRpcClient(
+            process: $mockProcess,
+            processLauncher: $mockProcessLauncher,
+            clock: $this->clock,
+            logger: $this->logger
+        );
+
+        $readProcessOutput = new \ReflectionMethod($client, 'readProcessOutput');
+        $readProcessOutput->invoke($client);
+    }
+
+    public function testReadProcessOutputClearsBuffersAcrossMultiplePolls(): void
+    {
+        $mockProcess = $this->createMock(Process::class);
+        $mockProcessLauncher = $this->createMock(ProcessLauncherInterface::class);
+
+        $mockProcess->method('isRunning')->willReturn(true);
+        $mockProcess->method('getPid')->willReturn(12345);
+        $mockProcess->method('getIncrementalOutput')->willReturn('');
+        $mockProcess->method('getIncrementalErrorOutput')->willReturn('');
+        $mockProcess->expects($this->exactly(3))->method('clearOutput');
+        $mockProcess->expects($this->exactly(3))->method('clearErrorOutput');
+        $mockProcessLauncher->method('getInputStream')->willReturn($this->mockInputStream);
+        $mockProcessLauncher->method('ensureRunning');
+
+        $client = new ProcessJsonRpcClient(
+            process: $mockProcess,
+            processLauncher: $mockProcessLauncher,
+            clock: $this->clock,
+            logger: $this->logger
+        );
+
+        $readProcessOutput = new \ReflectionMethod($client, 'readProcessOutput');
+        $readProcessOutput->invoke($client);
+        $readProcessOutput->invoke($client);
+        $readProcessOutput->invoke($client);
+    }
 }