diff --git a/src/alloc.c b/src/alloc.c
index efa35f58..9b441499 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -477,15 +477,16 @@ 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);
   const mi_page_t* const page = _mi_segment_page_of(segment, p);
-  const mi_block_t* const block = (const mi_block_t*)p;
-  const size_t size = mi_page_usable_size_of(page, block);
+  const mi_block_t* block = (const mi_block_t*)p;
   if (mi_unlikely(mi_page_has_aligned(page))) {
-    ptrdiff_t const adjust = (uint8_t*)p - (uint8_t*)_mi_page_ptr_unalign(segment,page,p);
+    block = _mi_page_ptr_unalign(segment, page, p);
+    size_t size = mi_page_usable_size_of(page, block);
+    ptrdiff_t const adjust = (uint8_t*)p - (uint8_t*)block;
     mi_assert_internal(adjust >= 0 && (size_t)adjust <= size);
     return (size - adjust);
   }
   else {
-    return size;
+    return mi_page_usable_size_of(page, block);
   }
 }
 
diff --git a/test/test-api.c b/test/test-api.c
index 166cfca6..e5827a93 100644
--- a/test/test-api.c
+++ b/test/test-api.c
@@ -152,6 +152,9 @@ int main() {
     }
     result = ok;
   });
+  CHECK_BODY("malloc-aligned5", {
+    void* p = mi_malloc_aligned(4097,4096); size_t usable = mi_usable_size(p); result = usable >= 4097 && usable < 10000; mi_free(p);
+  });
   CHECK_BODY("malloc-aligned-at1", {
     void* p = mi_malloc_aligned_at(48,32,0); result = (p != NULL && ((uintptr_t)(p) + 0) % 32 == 0); mi_free(p);
   });