diff --git a/modules/services/x11/desktop-managers/kde4.nix b/modules/services/x11/desktop-managers/kde4.nix
index 39aef7c6d56..e2adba6832a 100644
--- a/modules/services/x11/desktop-managers/kde4.nix
+++ b/modules/services/x11/desktop-managers/kde4.nix
@@ -172,7 +172,7 @@ in
     services.udisks = mkIf isKDE47 { enable = true; };
     services.upower = mkIf (isKDE47 && config.powerManagement.enable) { enable = true; };
 
-    security.pam.services = [ { name = "kde"; } ];
+    security.pam.services = [ { name = "kde"; allowNullPassword = true; } ];
 
   };
 
diff --git a/modules/services/x11/display-managers/kdm.nix b/modules/services/x11/display-managers/kdm.nix
index a819cadd270..fe7802100b2 100644
--- a/modules/services/x11/display-managers/kdm.nix
+++ b/modules/services/x11/display-managers/kdm.nix
@@ -111,7 +111,7 @@ in
         logsXsession = true;
       };
 
-    security.pam.services = [ { name = "kde"; } ];
+    security.pam.services = [ { name = "kde"; allowNullPassword = true; } ];
 
     users.extraUsers = singleton
       { name = "kdm";