diff --git a/tests/checks-nix-gc.nix b/tests/checks-nix-gc.nix
index 75700ccb..e3dccd7f 100644
--- a/tests/checks-nix-gc.nix
+++ b/tests/checks-nix-gc.nix
@@ -14,6 +14,6 @@ in
 
     echo checking nix-gc service in /Library/LaunchDaemons >&2
     grep "<string>org.nixos.nix-gc</string>" ${config.out}/Library/LaunchDaemons/org.nixos.nix-gc.plist
-    ! grep "<key>UserName</key>" ${config.out}/Library/LaunchDaemons/org.nixos.nix-gc.plist
+    (! grep "<key>UserName</key>" ${config.out}/Library/LaunchDaemons/org.nixos.nix-gc.plist)
   '';
 }
diff --git a/tests/nixpkgs-overlays.nix b/tests/nixpkgs-overlays.nix
index aa03bf11..59540ac3 100644
--- a/tests/nixpkgs-overlays.nix
+++ b/tests/nixpkgs-overlays.nix
@@ -10,7 +10,7 @@
 
   test = ''
     echo checking /bin/hello >&2
-    ! ${pkgs.hello}/bin/hello
+    (! ${pkgs.hello}/bin/hello)
   '';
 }
 
diff --git a/tests/services-nix-daemon.nix b/tests/services-nix-daemon.nix
index 5405d01f..3a217cbb 100644
--- a/tests/services-nix-daemon.nix
+++ b/tests/services-nix-daemon.nix
@@ -19,7 +19,7 @@ in
     grep "&amp;&amp;" ${config.out}/Library/LaunchDaemons/org.nixos.nix-daemon.plist
     grep "exec ${nix}/bin/nix-daemon</string>" ${config.out}/Library/LaunchDaemons/org.nixos.nix-daemon.plist
     grep "<key>KeepAlive</key>" ${config.out}/Library/LaunchDaemons/org.nixos.nix-daemon.plist
-    ! grep "<key>Sockets</key>" ${config.out}/Library/LaunchDaemons/org.nixos.nix-daemon.plist
+    (! grep "<key>Sockets</key>" ${config.out}/Library/LaunchDaemons/org.nixos.nix-daemon.plist)
 
     echo checking NIX_SSL_CERT_FILE in nix-daemon service >&2
     grep "<key>NIX_SSL_CERT_FILE</key>" ${config.out}/Library/LaunchDaemons/org.nixos.nix-daemon.plist
diff --git a/tests/services-nix-gc.nix b/tests/services-nix-gc.nix
index e28c3df2..4ef26b5e 100644
--- a/tests/services-nix-gc.nix
+++ b/tests/services-nix-gc.nix
@@ -15,11 +15,11 @@ in
     grep "<string>org.nixos.nix-gc</string>" ${config.out}/Library/LaunchDaemons/org.nixos.nix-gc.plist
     grep "<string>exec ${nix}/bin/nix-collect-garbage --delete-older-than 30d</string>" ${config.out}/Library/LaunchDaemons/org.nixos.nix-gc.plist
     grep "<key>UserName</key>" ${config.out}/Library/LaunchDaemons/org.nixos.nix-gc.plist
-    ! grep "<string>nixuser</string>" ${config.out}/Library/LaunchDaemons/org.nixos.nix-gc.plist
+    grep "<string>nixuser</string>" ${config.out}/Library/LaunchDaemons/org.nixos.nix-gc.plist
 
-    ! grep "<key>KeepAlive</key>" ${config.out}/Library/LaunchDaemons/org.nixos.nix-gc.plist
+    (! grep "<key>KeepAlive</key>" ${config.out}/Library/LaunchDaemons/org.nixos.nix-gc.plist)
 
     echo checking nix-gc validation >&2
-    ! grep "nix.gc.user = " ${config.out}/activate-user
+    (! grep "nix.gc.user = " ${config.out}/activate-user)
   '';
 }
diff --git a/tests/sockets-nix-daemon.nix b/tests/sockets-nix-daemon.nix
index 0eb09a77..606b7b6f 100644
--- a/tests/sockets-nix-daemon.nix
+++ b/tests/sockets-nix-daemon.nix
@@ -16,7 +16,7 @@ in
     grep "<string>/bin/wait4path" ${config.out}/Library/LaunchDaemons/org.nixos.nix-daemon.plist
     grep "&amp;&amp;" ${config.out}/Library/LaunchDaemons/org.nixos.nix-daemon.plist
     grep "exec ${nix}/bin/nix-daemon</string>" ${config.out}/Library/LaunchDaemons/org.nixos.nix-daemon.plist
-    ! grep "<key>KeepAlive</key>" ${config.out}/Library/LaunchDaemons/org.nixos.nix-daemon.plist
+    (! grep "<key>KeepAlive</key>" ${config.out}/Library/LaunchDaemons/org.nixos.nix-daemon.plist)
     grep "<key>Sockets</key>" ${config.out}/Library/LaunchDaemons/org.nixos.nix-daemon.plist
     grep "/nix/var/nix/daemon-socket/socket" ${config.out}/Library/LaunchDaemons/org.nixos.nix-daemon.plist
   '';