diff --git a/python/lvmscp/ln2.py b/python/lvmscp/ln2.py
index 1550a3a..e04fbcf 100644
--- a/python/lvmscp/ln2.py
+++ b/python/lvmscp/ln2.py
@@ -260,7 +260,7 @@ async def purge(
     check_lockfile()
 
     if check_pressure:
-        pressures = numpy.array((await get_pressures()).values())
+        pressures = numpy.array(list((await get_pressures()).values()))
         if numpy.any(numpy.isnan(pressures)) or numpy.any(pressures > PRESSURE_LIMIT):
             raise RuntimeError(
                 "One or more cameras have pressures "