diff --git a/CHANGELOG.md b/CHANGELOG.md
index bd685a51..d61be807 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - The `safe_run` method did unintentionally double-wrap the run method, if it already had a `make_action_safe` 
   decorator. This is now fixed.
 
+### Fixed
+- Under certain conditions hashing of an object defined in the `__main__` module failed.
+  This release implements a workaround for this issue, that should hopefully resolve most cases.
+
 ## [0.12.0] - 2022-11-15
 
 ### Added
diff --git a/tpcp/_hash.py b/tpcp/_hash.py
index 941e648b..05101ecc 100644
--- a/tpcp/_hash.py
+++ b/tpcp/_hash.py
@@ -22,12 +22,42 @@ def memoize(self, obj):
         return
 
     def hash(self, obj, return_digest=True):
+        """Get hash while handling some edgecases.
+
+        Namely, this implementation fixes the following issues:
+
+        - Because we skip memoization, we need to handle the case where the object is self-referential.
+          We just catch the error and raise a more descriptive error message.
+        - We need to handle the case where the object is defined in the `__main__` module.
+          For some reason, this can lead to pickle issues.
+          Based on some information I found, this should not happen, but it still does...
+          To fix it, we detect, when an object is defined in `__main__` and temporarily add it to the "real" module
+          representing the main function.
+          Afterwards we do some cleanup.
+          Not sure if really required, but it seems to work.
+          Overall very hacky, but I don't see a better way to fix this.
+
+        """
+        modules_modified = []
+        if getattr(obj, "__module__", None) == "__main__":
+            try:
+                name = obj.__name__
+            except AttributeError:
+                name = obj.__class__.__name__
+            mod = sys.modules["__main__"]
+            if not hasattr(mod, name):
+                modules_modified.append((mod, name))
+                setattr(mod, name, obj)
         try:
             return super().hash(obj, return_digest)
         except RecursionError as e:
             raise ValueError(
                 "The custom hasher used in tpcp does not support hashing of self-referential objects."
             ) from e
+        finally:
+            # Remove all new entries made to the main module.
+            for mod, name in modules_modified:
+                delattr(mod, name)
 
 
 class NoMemoizeNumpyHasher(NumpyHasher, NoMemoizeHasher):