diff --git a/include/mimalloc-atomic.h b/include/mimalloc-atomic.h
index 3a289feb..8b254d3e 100644
--- a/include/mimalloc-atomic.h
+++ b/include/mimalloc-atomic.h
@@ -179,7 +179,7 @@ static inline intptr_t mi_atomic_add(volatile _Atomic(intptr_t)* p, intptr_t add
 }
 static inline bool mi_atomic_cas_weak(volatile _Atomic(uintptr_t)* p, uintptr_t desired, uintptr_t expected) {
   MI_USING_STD
-  return atomic_compare_exchange_weak_explicit(p, &expected, desired, memory_order_acq_rel, memory_order_relaxed);
+  return atomic_compare_exchange_weak_explicit(p, &expected, desired, memory_order_release, memory_order_relaxed);
 }
 static inline bool mi_atomic_cas_strong(volatile _Atomic(uintptr_t)* p, uintptr_t desired, uintptr_t expected) {
   MI_USING_STD
diff --git a/src/alloc.c b/src/alloc.c
index 7e89a591..afc181dd 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -226,7 +226,7 @@ void mi_free(void* p) mi_attr_noexcept
 #endif
 
   const mi_segment_t* const segment = _mi_ptr_segment(p);
-  if (segment == NULL) return;  // checks for (p==NULL)
+  if (mi_unlikely(segment == NULL)) return;  // checks for (p==NULL)
 
 #if (MI_DEBUG>0)
   if (mi_unlikely(!mi_is_in_heap_region(p))) {