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
diff --git a/scripts/setup.py b/scripts/setup.py
index 692cfb7..07d52d1 100644
--- a/scripts/setup.py
+++ b/scripts/setup.py
@@ -18,6 +18,7 @@
         'intelhex>=2.2.1',
         'click',
         'cbor2',
+        'pyyaml',
     ],
     entry_points={
         "console_scripts": ["imgtool=imgtool.main:imgtool"]