diff --git a/nixos/tests/cups-pdf.nix b/nixos/tests/cups-pdf.nix
index 69f455a67c94..00623b14a9db 100644
--- a/nixos/tests/cups-pdf.nix
+++ b/nixos/tests/cups-pdf.nix
@@ -37,7 +37,7 @@
         machine.wait_until_succeeds(f"su - alice -c 'pdfinfo /var/spool/cups-pdf-{name}/users/alice/*.pdf'")
         machine.succeed(f"cp /var/spool/cups-pdf-{name}/users/alice/*.pdf /tmp/{name}.pdf")
         machine.copy_from_vm(f"/tmp/{name}.pdf", "")
-        run(f"${hostPkgs.imagemagickBig}/bin/convert -density 300 $out/{name}.pdf $out/{name}.jpeg", shell=True, check=True)
+        run(f"${lib.getExe hostPkgs.imagemagickBig} -density 300 $out/{name}.pdf $out/{name}.jpeg", shell=True, check=True)
         assert text.encode() in run(f"${lib.getExe hostPkgs.tesseract} $out/{name}.jpeg stdout", shell=True, check=True, capture_output=True).stdout
   '';
 
diff --git a/pkgs/by-name/cu/cups-pdf-to-pdf/package.nix b/pkgs/by-name/cu/cups-pdf-to-pdf/package.nix
index 97ec5a226c9d..ffcc45ecd974 100644
--- a/pkgs/by-name/cu/cups-pdf-to-pdf/package.nix
+++ b/pkgs/by-name/cu/cups-pdf-to-pdf/package.nix
@@ -21,7 +21,8 @@ stdenv.mkDerivation {
   buildInputs = [ cups ];
 
   postPatch = ''
-    sed -r 's|(gscall, size, ")cp |\1${coreutils}/bin/cp |' cups-pdf.c -i
+    substituteInPlace cups-pdf.c \
+      --replace-fail '"cp ' '"${lib.getExe' coreutils "cp"} '
   '';
 
   # gcc command line is taken from original cups-pdf's README file