diff --git a/src/osmo_gsm_tester/schema.py b/src/osmo_gsm_tester/schema.py
index 7fe6689..85c5fd6 100644
--- a/src/osmo_gsm_tester/schema.py
+++ b/src/osmo_gsm_tester/schema.py
@@ -136,6 +136,11 @@
         return
     raise ValueError('Unknown LTE RLC DRB Mode value: %r' % val)
 
+def duration(val):
+    if val.isdecimal() or val.endswith('m') or val.endswith('h'):
+        return
+    raise ValueError('Invalid duration value: %r' % val)
+
 INT = 'int'
 STR = 'str'
 UINT = 'uint'
@@ -157,6 +162,7 @@
 OSMO_TRX_CLOCK_REF = 'osmo_trx_clock_ref'
 LTE_TRANSMISSION_MODE = 'lte_transmission_mode'
 LTE_RLC_DRB_MODE = 'lte_rlc_drb_mode'
+DURATION = 'duration'
 
 SCHEMA_TYPES = {
         INT: int,
@@ -180,6 +186,7 @@
         OSMO_TRX_CLOCK_REF: osmo_trx_clock_ref,
         LTE_TRANSMISSION_MODE: lte_transmission_mode,
         LTE_RLC_DRB_MODE: lte_rlc_drb_mode,
+        DURATION: duration,
     }
 
 def validate(config, schema):