diff --git a/include/mimalloc.h b/include/mimalloc.h
index 368c22cc..7d3e3282 100644
--- a/include/mimalloc.h
+++ b/include/mimalloc.h
@@ -460,7 +460,7 @@ template<class T> struct mi_stl_allocator : public _mi_stl_allocator_common<T> {
 
   mi_stl_allocator()                                             mi_attr_noexcept = default;
   mi_stl_allocator(const mi_stl_allocator&)                      mi_attr_noexcept = default;
-  template<class U> mi_stl_allocator(const mi_stl_allocator<U>&) mi_attr_noexcept { }
+  template<class U> explicit mi_stl_allocator(const mi_stl_allocator<U>&) mi_attr_noexcept { }
   mi_stl_allocator  select_on_container_copy_construction() const { return *this; }
   void              deallocate(T* p, size_type) { mi_free(p); }
 
@@ -491,7 +491,7 @@ template<class T, bool _mi_destroy> struct _mi_heap_stl_allocator_common : publi
   using typename _mi_stl_allocator_common<T>::value_type;
   using typename _mi_stl_allocator_common<T>::pointer;
 
-  _mi_heap_stl_allocator_common(mi_heap_t* hp) : heap(hp) { }    /* will not delete nor destroy the passed in heap */
+  explicit _mi_heap_stl_allocator_common(mi_heap_t* hp) : heap(hp) { }    /* will not delete nor destroy the passed in heap */
 
   #if (__cplusplus >= 201703L)  // C++17
   mi_decl_nodiscard T* allocate(size_type count) { return static_cast<T*>(mi_heap_alloc_new_n(this->heap.get(), count, sizeof(T))); }
@@ -516,7 +516,7 @@ protected:
     this->heap.reset(hp, (_mi_destroy ? &heap_destroy : &heap_delete));  /* calls heap_delete/destroy when the refcount drops to zero */
   }
   _mi_heap_stl_allocator_common(const _mi_heap_stl_allocator_common& x) mi_attr_noexcept : heap(x.heap) { }
-  template<class U> _mi_heap_stl_allocator_common(const _mi_heap_stl_allocator_common<U, _mi_destroy>& x) mi_attr_noexcept : heap(x.heap) { }
+  template<class U> explicit _mi_heap_stl_allocator_common(const _mi_heap_stl_allocator_common<U, _mi_destroy>& x) mi_attr_noexcept : heap(x.heap) { }
 
 private:
   static void heap_delete(mi_heap_t* hp)  { if (hp != NULL) { mi_heap_delete(hp); } }
@@ -527,8 +527,8 @@ private:
 template<class T> struct mi_heap_stl_allocator : public _mi_heap_stl_allocator_common<T, false> {
   using typename _mi_heap_stl_allocator_common<T, false>::size_type;
   mi_heap_stl_allocator() : _mi_heap_stl_allocator_common<T, false>() { } // creates fresh heap that is deleted when the destructor is called
-  mi_heap_stl_allocator(mi_heap_t* hp) : _mi_heap_stl_allocator_common<T, false>(hp) { }  // no delete nor destroy on the passed in heap 
-  template<class U> mi_heap_stl_allocator(const mi_heap_stl_allocator<U>& x) mi_attr_noexcept : _mi_heap_stl_allocator_common<T, false>(x) { }
+  explicit mi_heap_stl_allocator(mi_heap_t* hp) : _mi_heap_stl_allocator_common<T, false>(hp) { }  // no delete nor destroy on the passed in heap 
+  template<class U> explicit mi_heap_stl_allocator(const mi_heap_stl_allocator<U>& x) mi_attr_noexcept : _mi_heap_stl_allocator_common<T, false>(x) { }
 
   mi_heap_stl_allocator select_on_container_copy_construction() const { return *this; }
   void deallocate(T* p, size_type) { mi_free(p); }
@@ -544,8 +544,8 @@ template<class T1, class T2> bool operator!=(const mi_heap_stl_allocator<T1>& x,
 template<class T> struct mi_heap_destroy_stl_allocator : public _mi_heap_stl_allocator_common<T, true> {
   using typename _mi_heap_stl_allocator_common<T, true>::size_type;
   mi_heap_destroy_stl_allocator() : _mi_heap_stl_allocator_common<T, true>() { } // creates fresh heap that is destroyed when the destructor is called
-  mi_heap_destroy_stl_allocator(mi_heap_t* hp) : _mi_heap_stl_allocator_common<T, true>(hp) { }  // no delete nor destroy on the passed in heap 
-  template<class U> mi_heap_destroy_stl_allocator(const mi_heap_destroy_stl_allocator<U>& x) mi_attr_noexcept : _mi_heap_stl_allocator_common<T, true>(x) { }
+  explicit mi_heap_destroy_stl_allocator(mi_heap_t* hp) : _mi_heap_stl_allocator_common<T, true>(hp) { }  // no delete nor destroy on the passed in heap 
+  template<class U> explicit mi_heap_destroy_stl_allocator(const mi_heap_destroy_stl_allocator<U>& x) mi_attr_noexcept : _mi_heap_stl_allocator_common<T, true>(x) { }
 
   mi_heap_destroy_stl_allocator select_on_container_copy_construction() const { return *this; }
   void deallocate(T*, size_type) { /* do nothing as we destroy the heap on destruct. */ }
diff --git a/include/mimalloc/atomic.h b/include/mimalloc/atomic.h
index fe418fab..deffe508 100644
--- a/include/mimalloc/atomic.h
+++ b/include/mimalloc/atomic.h
@@ -129,7 +129,9 @@ static inline void mi_atomic_maxi64_relaxed(volatile int64_t* p, int64_t x) {
 #elif defined(_MSC_VER)
 
 // MSVC C compilation wrapper that uses Interlocked operations to model C11 atomics.
+#ifndef WIN32_LEAN_AND_MEAN
 #define WIN32_LEAN_AND_MEAN
+#endif
 #include <windows.h>
 #include <intrin.h>
 #ifdef _WIN64
@@ -323,7 +325,9 @@ static inline void mi_atomic_yield(void) {
   std::this_thread::yield();
 }
 #elif defined(_WIN32)
+#ifndef WIN32_LEAN_AND_MEAN
 #define WIN32_LEAN_AND_MEAN
+#endif
 #include <windows.h>
 static inline void mi_atomic_yield(void) {
   YieldProcessor();
diff --git a/include/mimalloc/prim.h b/include/mimalloc/prim.h
index 9e560696..d1e25edf 100644
--- a/include/mimalloc/prim.h
+++ b/include/mimalloc/prim.h
@@ -133,7 +133,9 @@ static inline mi_threadid_t _mi_prim_thread_id(void) mi_attr_noexcept;
 
 #if defined(_WIN32)
 
+#ifndef WIN32_LEAN_AND_MEAN
 #define WIN32_LEAN_AND_MEAN
+#endif
 #include <windows.h>
 static inline mi_threadid_t _mi_prim_thread_id(void) mi_attr_noexcept {
   // Windows: works on Intel and ARM in both 32- and 64-bit
diff --git a/src/arena.c b/src/arena.c
index be1a9ebe..fbb94560 100644
--- a/src/arena.c
+++ b/src/arena.c
@@ -620,12 +620,12 @@ void _mi_arena_free(void* p, size_t size, size_t committed_size, mi_memid_t memi
     
     // checks
     if (arena == NULL) {
-      _mi_error_message(EINVAL, "trying to free from non-existent arena: %p, size %zu, memid: 0x%zx\n", p, size, memid);
+      _mi_error_message(EINVAL, "trying to free from non-existent arena: %p, size %zu, memid: %p\n", p, size, &memid);
       return;
     }
     mi_assert_internal(arena->field_count > mi_bitmap_index_field(bitmap_idx));
     if (arena->field_count <= mi_bitmap_index_field(bitmap_idx)) {
-      _mi_error_message(EINVAL, "trying to free from non-existent arena block: %p, size %zu, memid: 0x%zx\n", p, size, memid);
+      _mi_error_message(EINVAL, "trying to free from non-existent arena block: %p, size %zu, memid: %p\n", p, size, &memid);
       return;
     }
 
diff --git a/src/options.c b/src/options.c
index f52af8b8..67968ed0 100644
--- a/src/options.c
+++ b/src/options.c
@@ -114,7 +114,7 @@ void _mi_options_init(void) {
 
 mi_decl_nodiscard long mi_option_get(mi_option_t option) {
   mi_assert(option >= 0 && option < _mi_option_last);
-  if (option < 0 || option >= _mi_option_last) return 0;
+  if (option >= _mi_option_last) return 0;
   mi_option_desc_t* desc = &options[option];
   mi_assert(desc->option == option);  // index should match the option
   if mi_unlikely(desc->init == UNINIT) {
@@ -136,7 +136,7 @@ mi_decl_nodiscard size_t mi_option_get_size(mi_option_t option) {
 
 void mi_option_set(mi_option_t option, long value) {
   mi_assert(option >= 0 && option < _mi_option_last);
-  if (option < 0 || option >= _mi_option_last) return;
+  if (option >= _mi_option_last) return;
   mi_option_desc_t* desc = &options[option];
   mi_assert(desc->option == option);  // index should match the option
   desc->value = value;
@@ -145,7 +145,7 @@ void mi_option_set(mi_option_t option, long value) {
 
 void mi_option_set_default(mi_option_t option, long value) {
   mi_assert(option >= 0 && option < _mi_option_last);
-  if (option < 0 || option >= _mi_option_last) return;
+  if (option >= _mi_option_last) return;
   mi_option_desc_t* desc = &options[option];
   if (desc->init != INITIALIZED) {
     desc->value = value;