diff --git a/autotest/test_executables.py b/autotest/test_executables.py
index c06edc3..7f9f330 100644
--- a/autotest/test_executables.py
+++ b/autotest/test_executables.py
@@ -26,3 +26,6 @@ def test_access(exes):
     # .get() works too
     assert exes.get("not a target") is None
     assert exes.get("not a target", exes["pytest"]) == exes["pytest"]
+    # membership test
+    assert "not a target" not in exes
+    assert "pytest" in exes
diff --git a/modflow_devtools/executables.py b/modflow_devtools/executables.py
index 9e34149..59408ae 100644
--- a/modflow_devtools/executables.py
+++ b/modflow_devtools/executables.py
@@ -16,6 +16,9 @@ class Executables(SimpleNamespace):
     def __init__(self, **kwargs):
         super().__init__(**kwargs)
 
+    def __contains__(self, item):
+        return item in self.__dict__
+
     def __setitem__(self, key, item):
         self.__dict__[key] = item