diff --git a/muspy/base.py b/muspy/base.py
index 9151a1e..cee7bc3 100644
--- a/muspy/base.py
+++ b/muspy/base.py
@@ -528,7 +528,7 @@ class ComplexBase(Base):
 
     def __init__(self, **kwargs):
         Base.__init__(self, **kwargs)
-        self._flat = self._flat_generator()
+        self._flat = _GeneratorIterable(self._flat_generator)
 
     def __iadd__(
         self: ComplexBaseType, other: Union[ComplexBaseType, Iterable]
@@ -755,3 +755,13 @@ def _flat_generator(self) -> Iterable:
         value: list
         for _, _, value in self._traverse_lists(attr=None, recursive=True):
             yield from value
+
+
+class _GeneratorIterable:
+    """Turns a generator function into a reusable iterable."""
+
+    def __init__(self, generator_fn: Callable[[], Iterable]):
+        self._generator_fn = generator_fn
+
+    def __iter__(self):
+        return self._generator_fn()