diff --git a/common/sampling.cpp b/common/sampling.cpp
index 2f60be1943..526f036ff9 100644
--- a/common/sampling.cpp
+++ b/common/sampling.cpp
@@ -287,8 +287,8 @@ struct common_sampler * common_sampler_init(const struct llama_model * model, st
         }
     }
 
-    // reasoning budget sampler
-    if (!params.reasoning_budget_start.empty() && !params.reasoning_budget_end.empty()) {
+    // reasoning budget sampler (skip when budget is unlimited unless a lazy grammar is active, which needs rbudget for thinking-block suppression)
+    if (!params.reasoning_budget_start.empty() && !params.reasoning_budget_end.empty() && (params.grammar_lazy || params.reasoning_budget_tokens >= 0)) {
         rbudget = common_reasoning_budget_init(
             vocab,
             params.reasoning_budget_start,