diff --git a/src/mcp_esptool_server/components/qemu_manager.py b/src/mcp_esptool_server/components/qemu_manager.py
index ddc99b3..113d4e0 100644
--- a/src/mcp_esptool_server/components/qemu_manager.py
+++ b/src/mcp_esptool_server/components/qemu_manager.py
@@ -120,7 +120,7 @@ class QemuManager:
 
     def _allocate_port(self) -> int | None:
         """Find the next available TCP port for a QEMU instance"""
-        used_ports = {inst.tcp_port for inst in self.instances.values()}
+        used_ports = {inst.tcp_port for inst in self.instances.values() if inst.is_running}
         for offset in range(self.config.qemu_max_instances):
             port = self.config.qemu_base_port + offset
             if port not in used_ports:
@@ -434,6 +434,14 @@ class QemuManager:
             for inst in list(self.instances.values()):
                 stopped.append(await self._kill_instance(inst))
 
+        # Purge stopped instances that have no flash image on disk (nothing to reuse)
+        stale = [
+            k for k, v in self.instances.items()
+            if not v.is_running and not v.flash_image.exists()
+        ]
+        for k in stale:
+            del self.instances[k]
+
         return {
             "success": True,
             "stopped": [s for s in stopped if s],