diff --git a/pkgs/tools/security/swtpm/default.nix b/pkgs/tools/security/swtpm/default.nix
index de67a453fc5f..7f2352c7282c 100644
--- a/pkgs/tools/security/swtpm/default.nix
+++ b/pkgs/tools/security/swtpm/default.nix
@@ -33,6 +33,7 @@ stdenv.mkDerivation rec {
     perl # for pod2man
     autoreconfHook
   ];
+
   buildInputs = [
     libtpms
     openssl libtasn1 libseccomp
@@ -45,7 +46,7 @@ stdenv.mkDerivation rec {
     "--localstatedir=/var"
   ];
 
-  prePatch = ''
+  postPatch = ''
     # Makefile tries to create the directory /var/lib/swtpm-localca, which fails
     substituteInPlace samples/Makefile.am \
         --replace 'install-data-local:' 'do-not-execute:'