diff --git a/CMakeLists.txt b/CMakeLists.txt
index a2258128..475a5544 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -16,7 +16,7 @@ option(MI_BUILD_TESTS       "Build test executables" ON)
 
 include("cmake/mimalloc-config-version.cmake")
 
-set(mi_install_dir "lib/mimalloc-${mi_version}")
+set(mi_install_dir "${CMAKE_INSTALL_PREFIX}/lib/mimalloc-${mi_version}")
 
 set(mi_sources
     src/stats.c
diff --git a/include/mimalloc-atomic.h b/include/mimalloc-atomic.h
index c18f990f..ecdfba0d 100644
--- a/include/mimalloc-atomic.h
+++ b/include/mimalloc-atomic.h
@@ -241,7 +241,7 @@ static inline void mi_atomic_write(volatile _Atomic(uintptr_t)* p, uintptr_t x)
 #endif
 #elif defined(__wasi__)
   #include <sched.h>
-  static inline void mi_atomic_yield() {
+  static inline void mi_atomic_yield(void) {
     sched_yield();
   }
 #else
diff --git a/include/mimalloc-internal.h b/include/mimalloc-internal.h
index 77045a99..d727e563 100644
--- a/include/mimalloc-internal.h
+++ b/include/mimalloc-internal.h
@@ -101,6 +101,7 @@ uint8_t    _mi_bsr(uintptr_t x);                // bit-scan-right, used on BSD i
 void       _mi_heap_destroy_pages(mi_heap_t* heap);
 void       _mi_heap_collect_abandon(mi_heap_t* heap);
 uintptr_t  _mi_heap_random(mi_heap_t* heap);
+void       _mi_heap_set_default_direct(mi_heap_t* heap);
 
 // "stats.c"
 void       _mi_stats_done(mi_stats_t* stats);
diff --git a/src/heap.c b/src/heap.c
index d03925d5..1eb6811c 100644
--- a/src/heap.c
+++ b/src/heap.c
@@ -223,7 +223,7 @@ static void mi_heap_free(mi_heap_t* heap) {
   
   // reset default
   if (mi_heap_is_default(heap)) {
-    _mi_heap_default = heap->tld->heap_backing;
+    _mi_heap_set_default_direct(heap->tld->heap_backing);
   }
   // and free the used memory
   mi_free(heap);
@@ -354,8 +354,8 @@ mi_heap_t* mi_heap_set_default(mi_heap_t* heap) {
   mi_assert(mi_heap_is_initialized(heap));
   if (!mi_heap_is_initialized(heap)) return NULL;
   mi_assert_expensive(mi_heap_is_valid(heap));
-  mi_heap_t* old   = _mi_heap_default;
-  _mi_heap_default = heap;
+  mi_heap_t* old = mi_get_default_heap(); 
+  _mi_heap_set_default_direct(heap);
   return old;
 }
 
diff --git a/src/init.c b/src/init.c
index 72543b95..f9735462 100644
--- a/src/init.c
+++ b/src/init.c
@@ -90,6 +90,7 @@ const mi_heap_t _mi_heap_empty = {
   false
 };
 
+// the thread-local default heap for allocation
 mi_decl_thread mi_heap_t* _mi_heap_default = (mi_heap_t*)&_mi_heap_empty;
 
 
@@ -202,8 +203,8 @@ static bool _mi_heap_init(void) {
   if (mi_heap_is_initialized(_mi_heap_default)) return true;
   if (_mi_is_main_thread()) {
     // the main heap is statically allocated
-    _mi_heap_default = &_mi_heap_main;
-    mi_assert_internal(_mi_heap_default->tld->heap_backing == _mi_heap_default);
+    _mi_heap_set_default_direct(&_mi_heap_main);
+    mi_assert_internal(_mi_heap_default->tld->heap_backing == mi_get_default_heap());
   }
   else {
     // use `_mi_os_alloc` to allocate directly from the OS
@@ -228,18 +229,17 @@ static bool _mi_heap_init(void) {
     tld->os.reset_delay = reset_delay;
     memset(reset_delay, 0, sizeof(*reset_delay));
     reset_delay->capacity = MI_RESET_DELAY_SLOTS;
-    _mi_heap_default = heap;
+    _mi_heap_set_default_direct(heap);
   }
   return false;
 }
 
 // Free the thread local default heap (called from `mi_thread_done`)
-static bool _mi_heap_done(void) {
-  mi_heap_t* heap = _mi_heap_default;
+static bool _mi_heap_done(mi_heap_t* heap) {
   if (!mi_heap_is_initialized(heap)) return true;
 
   // reset default heap
-  _mi_heap_default = (_mi_is_main_thread() ? &_mi_heap_main : (mi_heap_t*)&_mi_heap_empty);
+  _mi_heap_set_default_direct(_mi_is_main_thread() ? &_mi_heap_main : (mi_heap_t*)&_mi_heap_empty);
 
   // todo: delete all non-backing heaps?
 
@@ -286,6 +286,8 @@ static bool _mi_heap_done(void) {
 // to set up the thread local keys.
 // --------------------------------------------------------
 
+static void _mi_thread_done(mi_heap_t* default_heap);
+
 #ifdef __wasi__
 // no pthreads in the WebAssembly Standard Interface
 #elif !defined(_WIN32)
@@ -300,14 +302,14 @@ static bool _mi_heap_done(void) {
   #include <fibersapi.h>
   static DWORD mi_fls_key;
   static void NTAPI mi_fls_done(PVOID value) {
-    if (value!=NULL) mi_thread_done();
+    if (value!=NULL) _mi_thread_done((mi_heap_t*)value);
   }
 #elif defined(MI_USE_PTHREADS)
   // use pthread locol storage keys to detect thread ending
   #include <pthread.h>
   static pthread_key_t mi_pthread_key;
   static void mi_pthread_done(void* value) {
-    if (value!=NULL) mi_thread_done();
+    if (value!=NULL) _mi_thread_done((mi_heap_t*)value);
   }
 #elif defined(__wasi__)
 // no pthreads in the WebAssembly Standard Interface
@@ -341,6 +343,8 @@ void mi_thread_init(void) mi_attr_noexcept
   mi_process_init();
 
   // initialize the thread local default heap
+  // (this will call `_mi_heap_set_default_direct` and thus set the
+  //  fiber/pthread key to a non-zero value, ensuring `_mi_thread_done` is called)
   if (_mi_heap_init()) return;  // returns true if already initialized
 
   // don't further initialize for the main thread
@@ -348,33 +352,38 @@ void mi_thread_init(void) mi_attr_noexcept
 
   _mi_stat_increase(&mi_get_default_heap()->tld->stats.threads, 1);
 
-  // set hooks so our mi_thread_done() will be called
-  #if defined(_WIN32) && defined(MI_SHARED_LIB)
-    // nothing to do as it is done in DllMain
-  #elif defined(_WIN32) && !defined(MI_SHARED_LIB)
-    FlsSetValue(mi_fls_key, (void*)(_mi_thread_id()|1)); // set to a dummy value so that `mi_fls_done` is called
-  #elif defined(MI_USE_PTHREADS)
-    pthread_setspecific(mi_pthread_key, (void*)(_mi_thread_id()|1)); // set to a dummy value so that `mi_pthread_done` is called
-  #endif
-
   //_mi_verbose_message("thread init: 0x%zx\n", _mi_thread_id());
 }
 
 void mi_thread_done(void) mi_attr_noexcept {
+  _mi_thread_done(mi_get_default_heap());
+}
+
+static void _mi_thread_done(mi_heap_t* heap) {
   // stats
-  mi_heap_t* heap = mi_get_default_heap();
   if (!_mi_is_main_thread() && mi_heap_is_initialized(heap))  {
     _mi_stat_decrease(&heap->tld->stats.threads, 1);
   }
-
   // abandon the thread local heap
-  if (_mi_heap_done()) return; // returns true if already ran
-
-  //if (!_mi_is_main_thread()) {
-  //  _mi_verbose_message("thread done: 0x%zx\n", _mi_thread_id());
-  //}
+  if (_mi_heap_done(heap)) return; // returns true if already ran
 }
 
+void _mi_heap_set_default_direct(mi_heap_t* heap)  {
+  mi_assert_internal(heap != NULL);
+  _mi_heap_default = heap;
+
+  // ensure the default heap is passed to `_mi_thread_done`
+  // setting to a non-NULL value also ensures `mi_thread_done` is called.
+  #if defined(_WIN32) && defined(MI_SHARED_LIB)
+    // nothing to do as it is done in DllMain
+  #elif defined(_WIN32) && !defined(MI_SHARED_LIB)
+    FlsSetValue(mi_fls_key, heap);
+  #elif defined(MI_USE_PTHREADS)
+    pthread_setspecific(mi_pthread_key, heap);
+  #endif
+}
+
+
 
 // --------------------------------------------------------
 // Run functions on process init/done, and thread init/done
@@ -449,7 +458,7 @@ void mi_process_init(void) mi_attr_noexcept {
   // access _mi_heap_default before setting _mi_process_is_initialized to ensure
   // that the TLS slot is allocated without getting into recursion on macOS
   // when using dynamic linking with interpose.
-  mi_heap_t* h = _mi_heap_default;
+  mi_heap_t* h = mi_get_default_heap();
   _mi_process_is_initialized = true;
 
   _mi_heap_main.thread_id = _mi_thread_id();
@@ -466,7 +475,7 @@ void mi_process_init(void) mi_attr_noexcept {
   #endif
   mi_thread_init();
   mi_stats_reset();  // only call stat reset *after* thread init (or the heap tld == NULL)
-  
+
   if (mi_option_is_enabled(mi_option_reserve_huge_os_pages)) {
     size_t pages = mi_option_get(mi_option_reserve_huge_os_pages);
     mi_reserve_huge_os_pages_interleave(pages, 0, pages*500);