diff --git a/src/AcDream.App/Rendering/Wb/WbDrawDispatcher.cs b/src/AcDream.App/Rendering/Wb/WbDrawDispatcher.cs
index 605b1e6..36ebdc9 100644
--- a/src/AcDream.App/Rendering/Wb/WbDrawDispatcher.cs
+++ b/src/AcDream.App/Rendering/Wb/WbDrawDispatcher.cs
@@ -772,7 +772,11 @@ public sealed unsafe class WbDrawDispatcher : IDisposable
         // §3 Q1/Q2 + §4 in
         // docs/superpowers/specs/2026-05-11-phase-n6-slice1-design.md.
         int gpuQuerySlot = _gpuQueryFrameIndex % GpuQueryRingDepth;
-        if (_gpuQueriesInitialized && _gpuQueryFrameIndex >= GpuQueryRingDepth)
+        // diag is part of the gate so the read/issue/increment trio stays
+        // symmetric — without it, toggling ACDREAM_WB_DIAG mid-session would
+        // freeze the frame counter (gated by diag below) while the read kept
+        // re-reading the same slot, producing duplicate stale samples.
+        if (diag && _gpuQueriesInitialized && _gpuQueryFrameIndex >= GpuQueryRingDepth)
         {
             _gl.GetQueryObject(_gpuQueryOpaque[gpuQuerySlot], QueryObjectParameterName.ResultAvailable, out int avail);
             if (avail != 0)