diff --git a/packages/nextcloud-mcp-server/package.nix b/packages/nextcloud-mcp-server/package.nix
index 1e319e1..3c2cb20 100644
--- a/packages/nextcloud-mcp-server/package.nix
+++ b/packages/nextcloud-mcp-server/package.nix
@@ -178,6 +178,12 @@ python3Packages.buildPythonApplication rec {
       --replace-quiet '">=2.4.5"' '""'
   '';
 
+  # PYTHONPATH from the host environment (e.g., mautrix bridge injecting
+  # Python 3.12 site-packages) causes C extension ABI mismatches on NixOS.
+  # The wrapper's own sys.path has the correct closure packages, so we
+  # unset the external PYTHONPATH to prevent contamination.
+  makeWrapperArgs = [ "--unset" "PYTHONPATH" ];
+
   dontCheckRuntimeDeps = true;
   catchConflicts = false;