diff --git a/tests/webapps-agnostic-docker.nix b/tests/webapps-agnostic-docker.nix
index 41ec232..dd95622 100644
--- a/tests/webapps-agnostic-docker.nix
+++ b/tests/webapps-agnostic-docker.nix
@@ -65,6 +65,8 @@ makeTest {
       virtualisation.memorySize = 8192;
       virtualisation.diskSize = 4096;
 
+      boot.extraSystemdUnitPaths = [ "/etc/systemd-mutable/system" ];
+
       # We can't download any substitutes in a test environment. To make tests
       # faster, we disable substitutes so that Nix does not waste any time by
       # attempting to download them.
diff --git a/tests/webapps-agnostic-s6-rc.nix b/tests/webapps-agnostic-s6-rc.nix
index 2acc6a2..1abd1da 100644
--- a/tests/webapps-agnostic-s6-rc.nix
+++ b/tests/webapps-agnostic-s6-rc.nix
@@ -62,6 +62,8 @@ makeTest {
       virtualisation.writableStore = true;
       virtualisation.memorySize = 1024;
 
+      boot.extraSystemdUnitPaths = [ "/etc/systemd-mutable/system" ];
+
       # We can't download any substitutes in a test environment. To make tests
       # faster, we disable substitutes so that Nix does not waste any time by
       # attempting to download them.
diff --git a/tests/webapps-agnostic-supervisord.nix b/tests/webapps-agnostic-supervisord.nix
index 1ac4fde..9514c2a 100644
--- a/tests/webapps-agnostic-supervisord.nix
+++ b/tests/webapps-agnostic-supervisord.nix
@@ -62,6 +62,8 @@ makeTest {
       virtualisation.writableStore = true;
       virtualisation.memorySize = 1024;
 
+      boot.extraSystemdUnitPaths = [ "/etc/systemd-mutable/system" ];
+
       # We can't download any substitutes in a test environment. To make tests
       # faster, we disable substitutes so that Nix does not waste any time by
       # attempting to download them.