diff --git a/packages/server/src/plugins/voice-mode.ts b/packages/server/src/plugins/voice-mode.ts
index 3e2f8cb5..66aff903 100644
--- a/packages/server/src/plugins/voice-mode.ts
+++ b/packages/server/src/plugins/voice-mode.ts
@@ -19,13 +19,13 @@ export class VoiceModeManager {
     })
   }
 
-  setEnabled(instanceId: string, connection: ClientConnectionRef, enabled: boolean): void {
+  setEnabled(instanceId: string, connection: ClientConnectionRef, enabled: boolean): boolean {
     if (enabled && !this.options.connections.isConnected(connection)) {
       this.options.logger.debug(
         { instanceId, clientId: connection.clientId, connectionId: connection.connectionId },
         "Ignoring voice mode enable for disconnected client connection",
       )
-      return
+      return false
     }
 
     const key = getConnectionKey(connection)
@@ -44,6 +44,7 @@ export class VoiceModeManager {
 
     this.options.logger.debug({ instanceId, clientId: connection.clientId, connectionId: connection.connectionId, enabled }, "Voice mode updated for client connection")
     this.publishIfChanged(instanceId)
+    return true
   }
 
   syncInstance(instanceId: string): void {
diff --git a/packages/server/src/server/routes/plugin.ts b/packages/server/src/server/routes/plugin.ts
index daa7630e..aef57007 100644
--- a/packages/server/src/server/routes/plugin.ts
+++ b/packages/server/src/server/routes/plugin.ts
@@ -66,11 +66,17 @@ export function registerPluginRoutes(app: FastifyInstance, deps: RouteDeps) {
     }
 
     const payload = VoiceModeStateSchema.parse(request.body ?? {})
-    deps.voiceModeManager.setEnabled(
+    const applied = deps.voiceModeManager.setEnabled(
       request.params.id,
       { clientId: payload.clientId, connectionId: payload.connectionId },
       payload.enabled,
     )
+
+    if (payload.enabled && !applied) {
+      reply.code(409).send({ error: "Client connection not active for voice mode enable" })
+      return
+    }
+
     return { enabled: payload.enabled }
   })