diff --git a/LLama/Sampling/DefaultSamplingPipeline.cs b/LLama/Sampling/DefaultSamplingPipeline.cs
index 27a4243c8..77d20e36a 100644
--- a/LLama/Sampling/DefaultSamplingPipeline.cs
+++ b/LLama/Sampling/DefaultSamplingPipeline.cs
@@ -246,7 +246,8 @@ public override LLamaToken Sample(SafeLLamaContextHandle ctx, int index)
                 }
                     
                 // Extended optimization : Apply the grammar to the TopK tokens and check if the selected token is valid
-                if (GrammarOptimization == GrammarOptimizationMode.Extended)
+                // Only run if TopK > 0
+                if (GrammarOptimization == GrammarOptimizationMode.Extended && TopK > 0)
                 {
                     // Calculate a safe TopK value
                     var safeTopK = Math.Min(TopK, nativeAll.Data.Length);