diff --git a/src/mem/alloc.h b/src/mem/alloc.h
index 23680f2..73a5844 100644
--- a/src/mem/alloc.h
+++ b/src/mem/alloc.h
@@ -922,8 +922,9 @@ namespace snmalloc
       if (super != nullptr)
         return super;
 
-      super = reinterpret_cast<Superslab*>(
-        large_allocator.template alloc<NoZero>(0, SUPERSLAB_SIZE));
+      super =
+        reinterpret_cast<Superslab*>(large_allocator.template alloc<NoZero>(
+          0, SUPERSLAB_SIZE, SUPERSLAB_SIZE));
 
       if (super == nullptr)
         return super;
@@ -1304,8 +1305,9 @@ namespace snmalloc
               sizeclass, rsize, size);
           });
         }
-        slab = reinterpret_cast<Mediumslab*>(
-          large_allocator.template alloc<NoZero>(0, SUPERSLAB_SIZE));
+        slab =
+          reinterpret_cast<Mediumslab*>(large_allocator.template alloc<NoZero>(
+            0, SUPERSLAB_SIZE, SUPERSLAB_SIZE));
 
         if (slab == nullptr)
           return nullptr;
@@ -1413,7 +1415,13 @@ namespace snmalloc
       size_t large_class = size_bits - SUPERSLAB_BITS;
       SNMALLOC_ASSERT(large_class < NUM_LARGE_CLASSES);
 
-      void* p = large_allocator.template alloc<zero_mem>(large_class, size);
+      size_t rsize = bits::one_at_bit(SUPERSLAB_BITS) << large_class;
+      // For superslab size, we always commit the whole range.
+      if (large_class == 0)
+        size = rsize;
+
+      void* p =
+        large_allocator.template alloc<zero_mem>(large_class, rsize, size);
       if (likely(p != nullptr))
       {
         chunkmap().set_large_size(p, size);
diff --git a/src/mem/largealloc.h b/src/mem/largealloc.h
index 1343300..ace16d0 100644
--- a/src/mem/largealloc.h
+++ b/src/mem/largealloc.h
@@ -290,12 +290,10 @@ namespace snmalloc
     LargeAlloc(MemoryProvider& mp) : memory_provider(mp) {}
 
     template<ZeroMem zero_mem = NoZero>
-    void* alloc(size_t large_class, size_t size)
+    void* alloc(size_t large_class, size_t rsize, size_t size)
     {
-      size_t rsize = bits::one_at_bit(SUPERSLAB_BITS) << large_class;
-      // For superslab size, we always commit the whole range.
-      if (large_class == 0)
-        size = rsize;
+      SNMALLOC_ASSERT(
+        (bits::one_at_bit(SUPERSLAB_BITS) << large_class) == rsize);
 
       void* p = memory_provider.pop_large_stack(large_class);