diff --git a/pyproject.toml b/pyproject.toml
index ad27022..cb9f9cc 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -135,6 +135,7 @@ addopts = [
     ]
 
 [tool.coverage.run]
+source = ["src/ngio"]
 omit = [
     "src/ngio/core/handler_protocol.py", # This is file only contains a protocol definition
     "src/ngio/ngff_meta/_meta_handler_protocol.py", # This is file only contains a protocol definition