diff --git a/src/mem/allocconfig.h b/src/mem/allocconfig.h
index 0ea5257..5bb03fb 100644
--- a/src/mem/allocconfig.h
+++ b/src/mem/allocconfig.h
@@ -100,7 +100,7 @@ namespace snmalloc
   static constexpr size_t MIN_ALLOC_SIZE = 2 * sizeof(void*);
   static constexpr size_t MIN_ALLOC_BITS = bits::ctz_const(MIN_ALLOC_SIZE);
 
-  // Slabs are 64 KiB unless constrained to 16 KiB.
+  // Slabs are 64 KiB unless constrained to 16 or even 8 KiB
   static constexpr size_t SLAB_BITS =
     USE_SMALL_CHUNKS ? 13 : (USE_LARGE_CHUNKS ? 16 : 14);
   static constexpr size_t SLAB_SIZE = 1 << SLAB_BITS;
diff --git a/src/mem/mediumslab.h b/src/mem/mediumslab.h
index 9dcfa66..905d760 100644
--- a/src/mem/mediumslab.h
+++ b/src/mem/mediumslab.h
@@ -25,7 +25,7 @@ namespace snmalloc
     uint16_t stack[SLAB_COUNT - 1];
 
   public:
-    static constexpr uint32_t header_size()
+    static constexpr size_t header_size()
     {
       static_assert(
         sizeof(Mediumslab) < OS_PAGE_SIZE,
@@ -34,9 +34,14 @@ namespace snmalloc
         sizeof(Mediumslab) < SLAB_SIZE,
         "Mediumslab header size must be less than the slab size");
 
-      // Always use a full page as the header, in order to get page sized
-      // alignment of individual allocations.
-      return OS_PAGE_SIZE;
+      /*
+       * Always use a full page or SLAB, whichever is smaller, in order
+       * to get good alignment of individual allocations.  Some platforms
+       * have huge minimum pages (e.g., Linux on PowerPC uses 64KiB) and
+       * our SLABs are occasionally small by comparison (e.g., in OE, when
+       * we take them to be 8KiB).
+       */
+      return bits::align_up(sizeof(Mediumslab), min(OS_PAGE_SIZE, SLAB_SIZE));
     }
 
     static Mediumslab* get(const void* p)