diff --git a/expat/lib/xmlparse.c b/expat/lib/xmlparse.c
--- a/expat/lib/xmlparse.c
+++ b/expat/lib/xmlparse.c
@@ -269,7 +269,9 @@ typedef struct {
 #define INIT_DATA_BUF_SIZE 1024
 #define INIT_ATTS_SIZE 16
 #define INIT_ATTS_VERSION 0xFFFFFFFF
-#define INIT_BLOCK_SIZE 1024
+/* BEGIN MOZILLA CHANGE (Avoid slop in poolGrow() allocations) */
+#define INIT_BLOCK_SIZE ((int)(1024 - (offsetof(BLOCK, s) / sizeof(XML_Char))))
+/* END MOZILLA CHANGE */
 #define INIT_BUFFER_SIZE 1024
 
 #define EXPAND_SPARE 24