diff --git a/src/osmo_gsm_tester/core/schema.py b/src/osmo_gsm_tester/core/schema.py
index 588c432..0b21e70 100644
--- a/src/osmo_gsm_tester/core/schema.py
+++ b/src/osmo_gsm_tester/core/schema.py
@@ -23,7 +23,7 @@
 from . import log
 from . import util
 
-KEY_RE = re.compile('[a-zA-Z][a-zA-Z0-9_]*')
+KEY_RE = re.compile('[a-zA-Z0-9][a-zA-Z0-9_]*')
 IPV4_RE = re.compile('([0-9]{1,3}.){3}[0-9]{1,3}')
 HWADDR_RE = re.compile('([0-9a-fA-F]{2}:){5}[0-9a-fA-F]{2}')
 IMSI_RE = re.compile('[0-9]{6,15}')