diff --git a/gwpy/detector/units.py b/gwpy/detector/units.py
index <HASH>..<HASH> 100644
--- a/gwpy/detector/units.py
+++ b/gwpy/detector/units.py
@@ -158,7 +158,7 @@ units.add_enabled_units(units.imperial)
 # 1) alternative names
 registry = units.get_current_unit_registry().registry
 for unit, aliases in [
-        (units.Unit('count'), ('counts')),
+        (units.Unit('ct'), ('counts',)),
         (units.Unit('Celsius'), ('Degrees_C', 'DegC')),
         (units.Unit('Fahrenheit'), ('Degrees_F', 'DegF')),
 ]:
gwpy.detector: fixed bug in unit aliasing

need commas to make a tuple!