diff --git a/Include/internal/pycore_mimalloc.h b/Include/internal/pycore_mimalloc.h
index dea88adac15db2..b38feda494207b 100644
--- a/Include/internal/pycore_mimalloc.h
+++ b/Include/internal/pycore_mimalloc.h
@@ -32,6 +32,11 @@ typedef enum {
 #  define MI_NO_THP 1
 // Do not use guarded allocations. The free-threaded GC does not support their block layout.
 #  define MI_GUARDED 0
+// Use 16 KiB pages instead of the default 64 KiB in 64-bit platforms.
+// TODO: 32-bit platforms may need tuning too.
+#  if SIZEOF_VOID_P == 8
+#    define MI_SEGMENT_SLICE_SHIFT 14
+#  endif
 #ifdef Py_DEBUG
 #  define MI_DEBUG 2
 #else