diff --git a/guppylang/decorator.py b/guppylang/decorator.py
index 0e2b627f..2a4244ad 100644
--- a/guppylang/decorator.py
+++ b/guppylang/decorator.py
@@ -33,7 +33,11 @@
 from guppylang.definition.struct import RawStructDef
 from guppylang.definition.ty import OpaqueTypeDef, TypeDef
 from guppylang.error import MissingModuleError, pretty_errors
-from guppylang.ipython_inspect import get_ipython_globals, is_running_ipython
+from guppylang.ipython_inspect import (
+    get_ipython_globals,
+    is_ipython_dummy_file,
+    is_running_ipython,
+)
 from guppylang.module import (
     GuppyModule,
     PyClass,
@@ -154,10 +158,8 @@ def _get_python_caller(self, fn: PyFunc | None = None) -> ModuleIdentifier:
             # Jupyter notebook cells all get different dummy filenames. However,
             # we want the whole notebook to correspond to a single implicit
             # Guppy module.
-            # TODO: Find a better way to detect if `filename` is a dummy name
-            #  generated by Jupyter
             filename = info.filename
-            if is_running_ipython() and not module and "ipykernel" in filename:
+            if is_running_ipython() and not module and is_ipython_dummy_file(filename):
                 filename = _JUPYTER_NOTEBOOK_MODULE
         module_path = Path(filename)
         return ModuleIdentifier(
diff --git a/guppylang/ipython_inspect.py b/guppylang/ipython_inspect.py
index 9726f7f0..5622c73c 100644
--- a/guppylang/ipython_inspect.py
+++ b/guppylang/ipython_inspect.py
@@ -12,6 +12,18 @@ def is_running_ipython() -> bool:
         return False
 
 
+def is_ipython_dummy_file(filename: str) -> bool:
+    """Checks whether a given filename is a dummy name generated for an IPython cell."""
+    # TODO: The approach below is false-positive prone. Figure out if there is a better
+    #  way to do this.
+    return (
+        # IPython cells have filenames like "<ipython-input-3-3e9b5833de21>"
+        filename.startswith("<ipython-input-")
+        # Jupyter cells have filenames like "/var/{...}/ipykernel_82076/61218616.py"
+        or "ipykernel_" in filename
+    )
+
+
 def get_ipython_cell_sources() -> list[str]:
     """Returns the source code of all cells in the running IPython session.