diff --git a/pkgs/os-specific/linux/systemd/default.nix b/pkgs/os-specific/linux/systemd/default.nix
index 4cda7191e4a..e6e5822c9ea 100644
--- a/pkgs/os-specific/linux/systemd/default.nix
+++ b/pkgs/os-specific/linux/systemd/default.nix
@@ -49,7 +49,14 @@ stdenv.mkDerivation rec {
       done
     '';
 
-  NIX_CFLAGS_COMPILE = "-DKBD_LOADKEYS=\"${kbd}/bin/loadkeys\" -DKBD_SETFONT=\"${kbd}/bin/setfont\" -fno-stack-protector";
+  NIX_CFLAGS_COMPILE =
+    [ "-DKBD_LOADKEYS=\"${kbd}/bin/loadkeys\""
+      "-DKBD_SETFONT=\"${kbd}/bin/setfont\""
+      # Can't say ${polkit}/bin/pkttyagent here because that would
+      # lead to a cyclic dependency.
+      "-DPOLKIT_AGENT_BINARY_PATH=\"/run/current-system/sw/bin/pkttyagent\""
+      "-fno-stack-protector"
+    ];
 
   makeFlags = "CPPFLAGS=-I${stdenv.gcc.libc}/include";