diff --git a/ptb3master.json b/ptb3master.json
index 2f6effb..e1c5c27 100644
--- a/ptb3master.json
+++ b/ptb3master.json
@@ -4,7 +4,7 @@
     "variant": "ptb3master",
     "hw_rev": "v1.1",
     "base": "master",
-    "_ext_ref_frequency": 100e6,
+    "ext_ref_frequency": 100e6,
     "core_addr": "10.34.16.100",
     "peripherals": [
         {