Arrange structure to match the common access patterns.
diff --git a/Modules/_collectionsmodule.c b/Modules/_collectionsmodule.c
index 8a43d9a..f175fca 100644
--- a/Modules/_collectionsmodule.c
+++ b/Modules/_collectionsmodule.c
@@ -48,8 +48,8 @@
 
 typedef struct BLOCK {
     struct BLOCK *leftlink;
-    struct BLOCK *rightlink;
     PyObject *data[BLOCKLEN];
+    struct BLOCK *rightlink;
 } block;
 
 #define MAXFREEBLOCKS 10