diff --git a/glib/gslice.c b/glib/gslice.c
index 8be5bad48..6ff3597bb 100644
--- a/glib/gslice.c
+++ b/glib/gslice.c
@@ -1273,13 +1273,18 @@ allocator_add_slab (Allocator *allocator,
   ChunkLink *chunk;
   SlabInfo *sinfo;
   gsize addr, padding, n_chunks, color = 0;
-  gsize page_size = allocator_aligned_page_size (allocator, SLAB_BPAGE_SIZE (allocator, chunk_size));
+  gsize page_size;
   int errsv;
-  /* allocate 1 page for the chunks and the slab */
-  gpointer aligned_memory = allocator_memalign (page_size, page_size - NATIVE_MALLOC_PADDING);
-  errsv = errno;
-  guint8 *mem = aligned_memory;
+  gpointer aligned_memory;
+  guint8 *mem;
   guint i;
+
+  page_size = allocator_aligned_page_size (allocator, SLAB_BPAGE_SIZE (allocator, chunk_size));
+  /* allocate 1 page for the chunks and the slab */
+  aligned_memory = allocator_memalign (page_size, page_size - NATIVE_MALLOC_PADDING);
+  errsv = errno;
+  mem = aligned_memory;
+
   if (!mem)
     {
       const gchar *syserr = strerror (errsv);