diff --git a/src/alloc.c b/src/alloc.c
index 607d15b6..57034522 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -387,34 +387,45 @@ static void mi_decl_noinline mi_free_generic(const mi_segment_t* segment, bool l
   _mi_free_block(page, local, block);
 }
 
+// Get the segment data belonging to a pointer
+// This is just a single `and` in assembly but does further checks in debug mode
+// (and secure mode) if this was a valid pointer.
+static inline mi_segment_t* mi_checked_ptr_segment(const void* p, const char* msg) 
+{
+  UNUSED(msg);
+#if (MI_DEBUG>0)
+  if (mi_unlikely(((uintptr_t)p & (MI_INTPTR_SIZE - 1)) != 0)) {
+    _mi_error_message(EINVAL, "%s: invalid (unaligned) pointer: %p\n", msg, p);
+    return NULL;
+  }
+#endif
+
+  mi_segment_t* const segment = _mi_ptr_segment(p);
+  if (mi_unlikely(segment == NULL)) return NULL;  // checks also for (p==NULL)
+
+#if (MI_DEBUG>0)
+  if (mi_unlikely(!mi_is_in_heap_region(p))) {
+    _mi_warning_message("%s: pointer might not point to a valid heap region: %p\n"
+      "(this may still be a valid very large allocation (over 64MiB))\n", msg, p);
+    if (mi_likely(_mi_ptr_cookie(segment) == segment->cookie)) {
+      _mi_warning_message("(yes, the previous pointer %p was valid after all)\n", p);
+    }
+  }
+#endif
+#if (MI_DEBUG>0 || MI_SECURE>=4)
+  if (mi_unlikely(_mi_ptr_cookie(segment) != segment->cookie)) {
+    _mi_error_message(EINVAL, "%s: pointer does not point to a valid heap space: %p\n", p);
+  }
+#endif
+  return segment;
+}
+
+
 // Free a block
 void mi_free(void* p) mi_attr_noexcept
 {
-#if (MI_DEBUG>0)
-  if (mi_unlikely(((uintptr_t)p & (MI_INTPTR_SIZE - 1)) != 0)) {
-    _mi_error_message(EINVAL, "trying to free an invalid (unaligned) pointer: %p\n", p);
-    return;
-  }
-#endif
-
-  const mi_segment_t* const segment = _mi_ptr_segment(p);
-  if (mi_unlikely(segment == NULL)) return;  // checks for (p==NULL)
-
-#if (MI_DEBUG!=0)
-  if (mi_unlikely(!mi_is_in_heap_region(p))) {
-    _mi_warning_message("possibly trying to free a pointer that does not point to a valid heap region: %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 %p was valid after all)\n", p);
-    } 
-  }
-#endif
-#if (MI_DEBUG!=0 || MI_SECURE>=4)
-  if (mi_unlikely(_mi_ptr_cookie(segment) != segment->cookie)) {
-    _mi_error_message(EINVAL, "trying to free a pointer that does not point to a valid heap space: %p\n", p);
-    return;
-  }
-#endif
+  const mi_segment_t* const segment = mi_checked_ptr_segment(p,"mi_free");
+  if (mi_unlikely(segment == NULL)) return; 
 
   const uintptr_t tid = _mi_thread_id();
   mi_page_t* const page = _mi_segment_page_of(segment, p);
@@ -473,9 +484,9 @@ bool _mi_free_delayed_block(mi_block_t* block) {
 }
 
 // Bytes available in a block
-size_t mi_usable_size(const void* p) mi_attr_noexcept {
-  if (p==NULL) return 0;
-  const mi_segment_t* const segment = _mi_ptr_segment(p);
+static size_t _mi_usable_size(const void* p, const char* msg) mi_attr_noexcept {
+  const mi_segment_t* const segment = mi_checked_ptr_segment(p,msg);
+  if (segment==NULL) return 0;
   const mi_page_t* const page = _mi_segment_page_of(segment, p);
   const mi_block_t* block = (const mi_block_t*)p;
   if (mi_unlikely(mi_page_has_aligned(page))) {
@@ -490,6 +501,10 @@ size_t mi_usable_size(const void* p) mi_attr_noexcept {
   }
 }
 
+size_t mi_usable_size(const void* p) mi_attr_noexcept {
+  return _mi_usable_size(p, "mi_usable_size");
+}
+
 
 // ------------------------------------------------------
 // ensure explicit external inline definitions are emitted!
@@ -513,7 +528,7 @@ void* _mi_externs[] = {
 
 void mi_free_size(void* p, size_t size) mi_attr_noexcept {
   UNUSED_RELEASE(size);
-  mi_assert(p == NULL || size <= mi_usable_size(p));
+  mi_assert(p == NULL || size <= _mi_usable_size(p,"mi_free_size"));
   mi_free(p);
 }
 
@@ -553,14 +568,14 @@ mi_decl_restrict void* mi_mallocn(size_t count, size_t size) mi_attr_noexcept {
 // Expand in place or fail
 void* mi_expand(void* p, size_t newsize) mi_attr_noexcept {
   if (p == NULL) return NULL;
-  size_t size = mi_usable_size(p);
+  size_t size = _mi_usable_size(p,"mi_expand");
   if (newsize > size) return NULL;
   return p; // it fits
 }
 
 void* _mi_heap_realloc_zero(mi_heap_t* heap, void* p, size_t newsize, bool zero) {
   if (p == NULL) return _mi_heap_malloc_zero(heap,newsize,zero);
-  size_t size = mi_usable_size(p);
+  size_t size = _mi_usable_size(p,"mi_realloc");
   if (newsize <= size && newsize >= (size / 2)) {
     return p;  // reallocation still fits and not more than 50% waste
   }
diff --git a/test/main-override-static.c b/test/main-override-static.c
index 9243fd21..f738c517 100644
--- a/test/main-override-static.c
+++ b/test/main-override-static.c
@@ -11,6 +11,7 @@ static void double_free1();
 static void double_free2();
 static void corrupt_free();
 static void block_overflow1();
+static void invalid_free();
 
 int main() {
   mi_version();
@@ -19,7 +20,8 @@ int main() {
   // double_free1();
   // double_free2();
   // corrupt_free();
-  block_overflow1();
+  // block_overflow1();
+  invalid_free();
 
   void* p1 = malloc(78);
   void* p2 = malloc(24);
@@ -43,6 +45,11 @@ int main() {
   return 0;
 }
 
+static void invalid_free() {
+  free((void*)0xBADBEEF);
+  realloc((void*)0xBADBEEF,10);
+}
+
 static void block_overflow1() {
   uint8_t* p = (uint8_t*)mi_malloc(17);
   p[18] = 0;