diff --git a/artiq/devices/pdq2/mediator.py b/artiq/devices/pdq2/mediator.py
index c73edf392..33fe24314 100644
--- a/artiq/devices/pdq2/mediator.py
+++ b/artiq/devices/pdq2/mediator.py
@@ -103,6 +103,9 @@ class _Frame:
     def _get_program(self):
         r = []
         for segment in self.segments:
+            if segment.duration < 2*trigger_duration:
+                raise ValueError(("Segment too short ({:g} s), trigger might "
+                                  "spill").format(segment.duration))
             segment_program = [
                 {
                     "dac_divider": dac_divider,
@@ -168,10 +171,10 @@ class CompoundPDQ2:
     def disarm(self):
         for frame in self.frames:
             frame._invalidate()
-        self.frames = []
-        self.armed = False
+        self.frames.clear()
         for dev in self.pdq2s:
             dev.park()
+        self.armed = False
 
     def get_program(self):
         return [f._get_program() for f in self.frames]
@@ -181,7 +184,6 @@ class CompoundPDQ2:
             raise ArmError()
         for frame in self.frames:
             frame._arm()
-        self.armed = True
 
         full_program = self.get_program()
         n = 0
@@ -203,6 +205,7 @@ class CompoundPDQ2:
             n += dn
         for pdq2 in self.pdq2s:
             pdq2.unpark()
+        self.armed = True
 
     def create_frame(self):
         if self.armed:
diff --git a/examples/master/repository/coredevice_examples/transport.py b/examples/master/repository/coredevice_examples/transport.py
index e60fe1989..ba367bdbc 100644
--- a/examples/master/repository/coredevice_examples/transport.py
+++ b/examples/master/repository/coredevice_examples/transport.py
@@ -17,8 +17,8 @@ class Transport(EnvExperiment):
 
         self.setattr_argument("wait_at_stop", NumberValue(100*us))
         self.setattr_argument("speed", NumberValue(1/(10*us)))
-        self.setattr_argument("repeats", NumberValue(100))
-        self.setattr_argument("bins", NumberValue(100))
+        self.repeats = int(self.get_argument("repeats", NumberValue(100)))
+        self.bins = int(self.get_argument("bins", NumberValue(100)))
 
         t = np.linspace(0, 10, 101)  # waveform time
         u = 1 - np.cos(np.pi*t/t[-1])