diff --git a/src/os.c b/src/os.c
index 3e8a9172..242a4eef 100644
--- a/src/os.c
+++ b/src/os.c
@@ -21,7 +21,7 @@ static mi_os_mem_config_t mi_os_mem_config = {
   0,      // large page size (usually 2MiB)
   4096,   // allocation granularity
   true,   // has overcommit?  (if true we use MAP_NORESERVE on mmap systems)
-  false   // must free whole?
+  false   // must free whole? (on mmap systems we can free anywhere in a mapped range, but on Windows we must free the entire span)
 };
 
 bool _mi_os_has_overcommit(void) {