diff --git a/numpydoc/numpydoc.py b/numpydoc/numpydoc.py
index 93cd975d..438fc8cc 100644
--- a/numpydoc/numpydoc.py
+++ b/numpydoc/numpydoc.py
@@ -215,7 +215,10 @@ def _clean_text_signature(sig):
     if sig is None:
         return None
     start_pattern = re.compile(r"^[^(]*\(")
-    start, end = start_pattern.search(sig).span()
+    try:
+        start, end = start_pattern.search(sig).span()
+    except TypeError:
+        return None
     start_sig = sig[start:end]
     sig = sig[end:-1]
     sig = re.sub(r'^\$(self|module|type)(,\s|$)','' , sig, count=1)
diff --git a/numpydoc/tests/test_numpydoc.py b/numpydoc/tests/test_numpydoc.py
index 77e75400..c20b71d6 100644
--- a/numpydoc/tests/test_numpydoc.py
+++ b/numpydoc/tests/test_numpydoc.py
@@ -66,6 +66,7 @@ def test_mangle_docstrings():
 
 def test_clean_text_signature():
     assert _clean_text_signature(None) is None
+    assert _clean_text_signature({"a": 1}) is None # i.e. not a string
     assert _clean_text_signature('func($self)') == 'func()'
     assert (_clean_text_signature('func($self, *args, **kwargs)')
             == 'func(*args, **kwargs)')