diff --git a/nixos/modules/system/boot/systemd.nix b/nixos/modules/system/boot/systemd.nix
index 78fe8c49fb0..05f8c8009bf 100644
--- a/nixos/modules/system/boot/systemd.nix
+++ b/nixos/modules/system/boot/systemd.nix
@@ -348,7 +348,8 @@ let
           [Service]
           ${let env = cfg.globalEnvironment // def.environment;
             in concatMapStrings (n:
-              let s = "Environment=\"${n}=${env.${n}}\"\n";
+              let s = optionalString (env."${n}" != null)
+                "Environment=\"${n}=${env.${n}}\"\n";
               in if stringLength s >= 2048 then throw "The value of the environment variable ‘${n}’ in systemd service ‘${name}.service’ is too long." else s) (attrNames env)}
           ${if def.reloadIfChanged then ''
             X-ReloadIfChanged=true