diff --git a/configtool/boardpanel.py b/configtool/boardpanel.py
index e449153..8376048 100644
--- a/configtool/boardpanel.py
+++ b/configtool/boardpanel.py
@@ -267,6 +267,18 @@ class BoardPanel(wx.Panel):
       self.parseDefineName(ln)
       self.parseDefineValue(ln)
 
+    # Set all boolean generic configuration items to False, so items not yet
+    # existing in the user configuration default to disabled.
+    #
+    # An alternative would be to allow both, enabled and disabled booleans
+    # in board.generic.h, which then allows to set an appropriate default for
+    # each #define. This was tried but conflicted with config file writing code
+    # below (disabled #defines were reset to the default, even when set
+    # differently in the GUI), so this would need adjustment, too.
+    for k in self.cfgValues.keys():
+      if isinstance(self.cfgValues[k], bool):
+        self.cfgValues[k] = False
+
     # Read the user configuration. This usually overwrites all of the items
     # read above, but not those missing in the user configuration, e.g.
     # when reading an older config.
diff --git a/configtool/printerpanel.py b/configtool/printerpanel.py
index 08ab132..7eb7211 100644
--- a/configtool/printerpanel.py
+++ b/configtool/printerpanel.py
@@ -232,6 +232,12 @@ class PrinterPanel(wx.Panel):
       self.parseDefineName(ln)
       self.parseDefineValue(ln)
 
+    # Set all boolean generic configuration items to False, so items not yet
+    # existing in the user configuration default to disabled.
+    for k in self.cfgValues.keys():
+      if isinstance(self.cfgValues[k], bool):
+        self.cfgValues[k] = False
+
     # Read the user configuration. This usually overwrites all of the items
     # read above, but not those missing in the user configuration, e.g.
     # when reading an older config.