diff --git a/modules/services/x11/display-managers/kdm.nix b/modules/services/x11/display-managers/kdm.nix
index 551710354429..18a6623eb851 100644
--- a/modules/services/x11/display-managers/kdm.nix
+++ b/modules/services/x11/display-managers/kdm.nix
@@ -26,6 +26,8 @@ let
 
       [X-:*-Core]
       ServerCmd=${dmcfg.xserverBin} ${dmcfg.xserverArgs}
+      # The default timeout (15) is too short in a heavily loaded boot process.
+      ServerTimeout=60
       # Needed to prevent the X server from dying on logout and not coming back:
       TerminateServer=true