diff --git a/bin/readme.md b/bin/readme.md
index f08b2e87..18831d04 100644
--- a/bin/readme.md
+++ b/bin/readme.md
@@ -3,7 +3,7 @@
 <span id="override_on_windows">We use a separate redirection DLL to override mimalloc on Windows</span> 
 such that we redirect all malloc/free calls that go through the (dynamic) C runtime allocator, 
 including those from other DLL's or libraries. As it intercepts all allocation calls on a low level, 
-it can be used reliably on large programs that include other 3rd party components.
+it can be used on large programs that include other 3rd party components.
 There are four requirements to make the overriding work well:
 
 1. Use the C-runtime library as a DLL (using the `/MD` or `/MDd` switch).
diff --git a/readme.md b/readme.md
index f1dd3965..30875b63 100644
--- a/readme.md
+++ b/readme.md
@@ -20,7 +20,8 @@ without code changes, for example, on dynamically linked ELF-based systems (Linu
 ```
 > LD_PRELOAD=/usr/lib/libmimalloc.so  myprogram
 ```
-It also includes a robust way to override the default allocator in [Windows](#override_on_windows). Notable aspects of the design include:
+It also includes a way to dynamically override the default allocator in [Windows](#override_on_windows). 
+Notable aspects of the design include:
 
 - __small and consistent__: the library is about 10k LOC using simple and
   consistent data structures. This makes it very suitable
@@ -478,7 +479,7 @@ the [shell](https://stackoverflow.com/questions/43941322/dyld-insert-libraries-i
 <span id="override_on_windows">We use a separate redirection DLL to override mimalloc on Windows</span> 
 such that we redirect all malloc/free calls that go through the (dynamic) C runtime allocator, 
 including those from other DLL's or libraries. As it intercepts all allocation calls on a low level, 
-it can be used reliably on large programs that include other 3rd party components.
+it can be used on large programs that include other 3rd party components.
 There are four requirements to make the overriding work well:
 
 1. Use the C-runtime library as a DLL (using the `/MD` or `/MDd` switch).
diff --git a/src/segment-map.c b/src/segment-map.c
index 43cb3bd9..2f68f8c4 100644
--- a/src/segment-map.c
+++ b/src/segment-map.c
@@ -28,9 +28,9 @@ terms of the MIT license. A copy of the license can be found in the file
 #define MI_SEGMENT_MAP_PART_SIZE      (MI_INTPTR_SIZE*MI_KiB - 128)      // 128 > sizeof(mi_memid_t) ! 
 #define MI_SEGMENT_MAP_PART_BITS      (8*MI_SEGMENT_MAP_PART_SIZE)
 #define MI_SEGMENT_MAP_PART_ENTRIES   (MI_SEGMENT_MAP_PART_SIZE / MI_INTPTR_SIZE)
-#define MI_SEGMENT_MAP_PART_BIT_SPAN  (MI_SEGMENT_ALIGN)
+#define MI_SEGMENT_MAP_PART_BIT_SPAN  (MI_SEGMENT_ALIGN)                 // memory area covered by 1 bit
 
-#if (MI_SEGMENT_PART_BITS < (MI_SEGMENT_MAP_MAX_ADDRESS / MI_SEGMENT_MAP_PART_BIT_SPAN)) // prevent overflow on 32-bit (issue #1017)
+#if (MI_SEGMENT_MAP_PART_BITS < (MI_SEGMENT_MAP_MAX_ADDRESS / MI_SEGMENT_MAP_PART_BIT_SPAN)) // prevent overflow on 32-bit (issue #1017)
 #define MI_SEGMENT_MAP_PART_SPAN      (MI_SEGMENT_MAP_PART_BITS * MI_SEGMENT_MAP_PART_BIT_SPAN)
 #else
 #define MI_SEGMENT_MAP_PART_SPAN      MI_SEGMENT_MAP_MAX_ADDRESS
@@ -58,7 +58,7 @@ static mi_segmap_part_t* mi_segment_map_index_of(const mi_segment_t* segment, bo
   mi_segmap_part_t* part = mi_atomic_load_ptr_relaxed(mi_segmap_part_t, &mi_segment_map[segindex]);
 
   // allocate on demand to reduce .bss footprint
-  if (part == NULL) {
+  if mi_unlikely(part == NULL) {
     if (!create_on_demand) return NULL;
     mi_memid_t memid;
     part = (mi_segmap_part_t*)_mi_os_alloc(sizeof(mi_segmap_part_t), &memid);