diff --git a/terminatorlib/terminal.py b/terminatorlib/terminal.py
index 2aaf58d7..78b48e71 100644
--- a/terminatorlib/terminal.py
+++ b/terminatorlib/terminal.py
@@ -750,7 +750,7 @@ def reconfigure(self, _widget=None):
             self.bgcolor.parse(self.config['background_color'])
 
         if self.config['background_type'] in ('transparent', 'image'):
-            self.bgcolor.alpha = self.config['background_darkness']
+            self.bgcolor.alpha = float(self.config['background_darkness'])
         else:
             self.bgcolor.alpha = 1