diff --git a/nixos/modules/system/boot/loader/systemd-boot/systemd-boot.nix b/nixos/modules/system/boot/loader/systemd-boot/systemd-boot.nix
index 2d5c7cc9caa0..84a654916441 100644
--- a/nixos/modules/system/boot/loader/systemd-boot/systemd-boot.nix
+++ b/nixos/modules/system/boot/loader/systemd-boot/systemd-boot.nix
@@ -216,7 +216,7 @@ in {
     consoleMode = mkOption {
       default = "keep";
 
-      type = types.enum [ "0" "1" "2" "auto" "max" "keep" ];
+      type = types.enum [ "0" "1" "2" "5" "auto" "max" "keep" ];
 
       description = ''
         The resolution of the console. The following values are valid:
@@ -224,6 +224,7 @@ in {
         - `"0"`: Standard UEFI 80x25 mode
         - `"1"`: 80x50 mode, not supported by all devices
         - `"2"`: The first non-standard mode provided by the device firmware, if any
+        - `"5"`: Applicable for SteamDeck where this mode represent horizontal mode
         - `"auto"`: Pick a suitable mode automatically using heuristics
         - `"max"`: Pick the highest-numbered available mode
         - `"keep"`: Keep the mode selected by firmware (the default)