diff --git a/tests/common/server.nix b/tests/common/server.nix
index 34476df..561d1bb 100644
--- a/tests/common/server.nix
+++ b/tests/common/server.nix
@@ -7,6 +7,15 @@
       certificateScheme = "selfsigned";
     };
 
+    # Prevent tests deadlocking on DNS requests which will never succeed.
+    services.rspamd.locals."options.inc".text = ''
+      dns {
+        nameservers = ["127.0.0.1"];
+        timeout = 0.0s;
+        retransmits = 0;
+      }
+    '';
+
     # Enable more verbose logging (required for, e.g., sieve testing)
     services.dovecot2.extraConfig = lib.mkAfter ''
       mail_debug = yes