diff --git a/pkgs/development/python-modules/pure-pcapy3/default.nix b/pkgs/development/python-modules/pure-pcapy3/default.nix
index ad405c593853..8e07377723e0 100644
--- a/pkgs/development/python-modules/pure-pcapy3/default.nix
+++ b/pkgs/development/python-modules/pure-pcapy3/default.nix
@@ -16,6 +16,12 @@ buildPythonPackage rec {
     hash = "sha256-uZ5F8W1K1BDrXrvH1dOeNT1+2n6G8K1S5NxcRaez6pI=";
   };
 
+  # fixes: AttributeError: 'FixupTest' object has no attribute 'assertEquals'. Did you mean: 'assertEqual'?
+  postPatch = ''
+    substituteInPlace test/__init__.py \
+      --replace-fail "assertEquals" "assertEqual"
+  '';
+
   pythonImportsCheck = [
     "pure_pcapy"
   ];