diff --git a/src/alloc.c b/src/alloc.c
index bac925ee..099bdbad 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -211,8 +211,11 @@ void mi_free(void* p) mi_attr_noexcept
 
 #if (MI_DEBUG>0)
   if (mi_unlikely(!mi_is_in_heap_region(p))) {
-    _mi_warning_message("possibly trying to mi_free a pointer that does not point to a valid heap region: %p\n"
+    _mi_warning_message("possibly trying to mi_free a pointer that does not point to a valid heap region: 0x%p\n"
       "(this may still be a valid very large allocation (over 64MiB))\n", p);
+    if (mi_likely(_mi_ptr_cookie(segment) == segment->cookie)) {
+      _mi_warning_message("(yes, the previous pointer 0x%p was valid after all)\n", p);
+    }
   }
   if (mi_unlikely(_mi_ptr_cookie(segment) != segment->cookie)) {
     _mi_error_message("trying to mi_free a pointer that does not point to a valid heap space: %p\n", p);