diff --git a/csp/impl/wiring/base_parser.py b/csp/impl/wiring/base_parser.py
index 5b90fc6d6..b154be55f 100644
--- a/csp/impl/wiring/base_parser.py
+++ b/csp/impl/wiring/base_parser.py
@@ -1,6 +1,7 @@
 import ast
 import copy
 import inspect
+import re
 import sys
 import textwrap
 import typing
@@ -87,6 +88,55 @@ def wrapper(*args, **kwargs):
     return wrapper
 
 
+def _get_source_from_interpreter_function(raw_func):
+    try:
+        import readline
+    except ImportError as exc:
+        raise OSError(
+            "Could not get source code for interpreter-defined function without `pyreadline` installed."
+        ) from exc
+
+    current_interpreter_history = readline.get_current_history_length()
+
+    try:
+        search_pattern = re.compile(r"^(\s*def\s*" + raw_func.__name__ + r"\s*\()")
+        decorator_pattern = re.compile(r"^(\s*@)")
+        code_object = raw_func.__func__ if inspect.ismethod(raw_func) else raw_func.__code__
+    except Exception:
+        raise OSError("Could not get source code for interpreter-defined function.")
+
+    if not hasattr(code_object, "co_firstlineno"):
+        raise OSError("Could not find function definition for interpreter-defined function.")
+
+    reassembled_function = ""
+    starting_index_of_function = current_interpreter_history
+
+    # walk back through history to find the function definition
+    while starting_index_of_function > 0:
+        line = readline.get_history_item(starting_index_of_function)
+
+        # if its a def name_of_function(...
+        if search_pattern.match(line):
+            # reassemble function
+            for i in range(starting_index_of_function, current_interpreter_history + 1):
+                reassembled_function += f"{readline.get_history_item(i)}\n"
+
+            for line_number_with_decorator in range(starting_index_of_function - 1, -1, -1):
+                if decorator_pattern.match(readline.get_history_item(line_number_with_decorator)):
+                    reassembled_function = (
+                        f"{readline.get_history_item(line_number_with_decorator)}\n" + reassembled_function
+                    )
+                else:
+                    break
+            break
+        starting_index_of_function -= 1
+
+    if reassembled_function == "":
+        raise OSError("Could not find function definition for interpreter-defined function.")
+
+    return reassembled_function
+
+
 class BaseParser(ast.NodeTransformer, metaclass=ABCMeta):
     _DEBUG_PARSE = False
 
@@ -109,7 +159,15 @@ def __init__(self, name, raw_func, func_frame, debug_print=False):
         self._func_globals_modified["csp"] = csp
         self._func_globals_modified.update(self._func_frame.f_globals)
 
-        source = textwrap.dedent(inspect.getsource(raw_func))
+        if raw_func.__code__.co_filename == "<stdin>":
+            raw_source = _get_source_from_interpreter_function(raw_func)
+        elif raw_func.__code__.co_filename == "<string>":
+            raise OSError("Could not find function definition for exec'd function.")
+        else:
+            raw_source = inspect.getsource(raw_func)
+
+        source = textwrap.dedent(raw_source)
+
         body = ast.parse(source)
         self._funcdef = body.body[0]
         self._type_annotation_normalizer.normalize_type_annotations(self._funcdef)