diff --git a/lib/blockchain.py b/lib/blockchain.py
index 434d6dca..3c95e2eb 100644
--- a/lib/blockchain.py
+++ b/lib/blockchain.py
@@ -29,11 +29,11 @@ from . import bitcoin
 from . import constants
 from .bitcoin import *
 
-HDR_LEN = 1487
-HDR_EH_192_7_LEN = 543
+HDR_LEN = 1344
+HDR_EH_192_7_LEN = 400
 CHUNK_LEN = 100
-BUBBLES_ACTIVATION_HEIGHT = 585318
-DIFFADJ_ACTIVATION_HEIGHT = 585322
+BUBBLES_ACTIVATION_HEIGHT = 618000
+DIFFADJ_ACTIVATION_HEIGHT = 618018
 
 MAX_TARGET = 0x0007FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF
 POW_AVERAGING_WINDOW = 17