diff --git a/packages/app/src/components/composer.tsx b/packages/app/src/components/composer.tsx
index 1914bae49..dc29e28fd 100644
--- a/packages/app/src/components/composer.tsx
+++ b/packages/app/src/components/composer.tsx
@@ -756,7 +756,8 @@ function ComposerRightControlsSlot({
   ...voiceProps
 }: ComposerRightControlsSlotProps) {
   const hideVoiceForCompactInput = isCompact && hasSendableContent;
-  const showVoiceModeButton = !isVoiceModeForAgent && hasAgent && !hideVoiceForCompactInput;
+  const showVoiceModeButton =
+    !isVoiceModeForAgent && hasAgent && !isAgentRunning && !hideVoiceForCompactInput;
   const shouldShowCancelButton = isAgentRunning && !hasSendableContent && !isProcessing;
   if (!showVoiceModeButton && !shouldShowCancelButton) return null;
   return (
diff --git a/packages/app/src/components/message-input.tsx b/packages/app/src/components/message-input.tsx
index 3fc41f11d..ed4409b2a 100644
--- a/packages/app/src/components/message-input.tsx
+++ b/packages/app/src/components/message-input.tsx
@@ -799,6 +799,7 @@ interface ToggleRealtimeVoiceContext {
   voiceAgentId: string | undefined;
   isConnected: boolean;
   disabled: boolean;
+  isAgentRunning: boolean;
   handleStopRealtimeVoice: () => Promise<unknown> | void;
   toast: { error: (msg: string) => void };
 }
@@ -812,6 +813,10 @@ function toggleRealtimeVoiceImpl(ctx: ToggleRealtimeVoiceContext): void {
     void ctx.handleStopRealtimeVoice();
     return;
   }
+  if (ctx.isAgentRunning) {
+    ctx.toast.error("Interrupt the agent before starting voice mode");
+    return;
+  }
   void ctx.voice.startVoice(ctx.voiceServerId, ctx.voiceAgentId).catch((error) => {
     console.error("[MessageInput] Failed to start realtime voice", error);
     const message = extractErrorMessage(error);
@@ -1450,10 +1455,20 @@ export const MessageInput = forwardRef<MessageInputRef, MessageInputProps>(
         voiceAgentId,
         isConnected,
         disabled,
+        isAgentRunning,
         handleStopRealtimeVoice,
         toast,
       });
-    }, [disabled, handleStopRealtimeVoice, isConnected, toast, voice, voiceAgentId, voiceServerId]);
+    }, [
+      disabled,
+      handleStopRealtimeVoice,
+      isAgentRunning,
+      isConnected,
+      toast,
+      voice,
+      voiceAgentId,
+      voiceServerId,
+    ]);
 
     const minimizeInputHeight = useCallback(() => {
       inputHeightRef.current = MIN_INPUT_HEIGHT;