diff --git a/scripts/imgtool.nix b/scripts/imgtool.nix
index ea9ba8b..e5dc2fd 100644
--- a/scripts/imgtool.nix
+++ b/scripts/imgtool.nix
@@ -21,6 +21,7 @@
       python37.pkgs.intelhex
       python37.pkgs.setuptools
       python37.pkgs.cbor2
+      python37.pkgs.pyyaml
     ]
   );
 in