diff --git a/src/memline.c b/src/memline.c
index 7cbe559..7acea13 100644
--- a/src/memline.c
+++ b/src/memline.c
@@ -130,7 +130,7 @@
 #define DB_INDEX_MASK	(~DB_MARKED)
 
 #define INDEX_SIZE  (sizeof(unsigned))	    // size of one db_index entry
-#define HEADER_SIZE (sizeof(DATA_BL) - INDEX_SIZE)  // size of data block header
+#define HEADER_SIZE (offsetof(DATA_BL, db_index))  // size of data block header
 
 #define B0_FNAME_SIZE_ORG	900	// what it was in older versions
 #define B0_FNAME_SIZE_NOCRYPT	898	// 2 bytes used for other things
@@ -4162,8 +4162,9 @@
     pp = (PTR_BL *)(hp->bh_data);
     pp->pb_id = PTR_ID;
     pp->pb_count = 0;
-    pp->pb_count_max = (short_u)((mfp->mf_page_size - sizeof(PTR_BL))
-							/ sizeof(PTR_EN) + 1);
+    pp->pb_count_max =
+	(short_u)((mfp->mf_page_size - offsetof(PTR_BL, pb_pointer))
+							     / sizeof(PTR_EN));
 
     return hp;
 }