diff --git a/src/silx/gui/plot/actions/control.py b/src/silx/gui/plot/actions/control.py
index b48bef0a1f..c774032cca 100755
--- a/src/silx/gui/plot/actions/control.py
+++ b/src/silx/gui/plot/actions/control.py
@@ -333,7 +333,7 @@ def __init__(self, plot, parent=None):
 
     def setColormapDialog(self, dialog):
         """Set a specific colormap dialog instead of using the default one."""
-        assert(colormapDialog is not None)
+        assert colormapDialog is not None
         if self._dialog is not None:
             self._dialog.visibleChanged.disconnect(self._dialogVisibleChanged)