diff --git a/include/mimalloc.h b/include/mimalloc.h
index 08af2eb9..1f6f1ef7 100644
--- a/include/mimalloc.h
+++ b/include/mimalloc.h
@@ -108,8 +108,8 @@ mi_decl_export mi_decl_allocator void* mi_reallocf(void* p, size_t newsize)
 mi_decl_export size_t mi_usable_size(const void* p)   mi_attr_noexcept;
 mi_decl_export size_t mi_good_size(size_t size)       mi_attr_noexcept;
 
-typedef void (mi_deferred_free_fun)(bool force, unsigned long long heartbeat);
-mi_decl_export void mi_register_deferred_free(mi_deferred_free_fun* deferred_free) mi_attr_noexcept;
+typedef void (mi_deferred_free_fun)(bool force, unsigned long long heartbeat, void* arg);
+mi_decl_export void mi_register_deferred_free(mi_deferred_free_fun* deferred_free, void* arg) mi_attr_noexcept;
 
 typedef void (mi_output_fun)(const char* msg, void* arg);
 mi_decl_export void mi_register_output(mi_output_fun* out, void* arg) mi_attr_noexcept;
diff --git a/src/page.c b/src/page.c
index 7491bd61..6a6e09d6 100644
--- a/src/page.c
+++ b/src/page.c
@@ -764,18 +764,20 @@ static inline mi_page_t* mi_find_free_page(mi_heap_t* heap, size_t size) {
 ----------------------------------------------------------- */
 
 static mi_deferred_free_fun* volatile deferred_free = NULL;
+static volatile _Atomic(void*) deferred_arg; // = NULL
 
 void _mi_deferred_free(mi_heap_t* heap, bool force) {
   heap->tld->heartbeat++;
   if (deferred_free != NULL && !heap->tld->recurse) {
     heap->tld->recurse = true;
-    deferred_free(force, heap->tld->heartbeat);
+    deferred_free(force, heap->tld->heartbeat, mi_atomic_read_ptr_relaxed(&deferred_arg));
     heap->tld->recurse = false;
   }
 }
 
-void mi_register_deferred_free(mi_deferred_free_fun* fn) mi_attr_noexcept {
+void mi_register_deferred_free(mi_deferred_free_fun* fn, void* arg) mi_attr_noexcept {
   deferred_free = fn;
+  mi_atomic_write_ptr(&deferred_arg, arg);
 }