diff --git a/pyhanko/sign/diff_analysis/rules/form_field_rules.py b/pyhanko/sign/diff_analysis/rules/form_field_rules.py
index 4d0e798f..1e98a153 100644
--- a/pyhanko/sign/diff_analysis/rules/form_field_rules.py
+++ b/pyhanko/sign/diff_analysis/rules/form_field_rules.py
@@ -661,7 +661,11 @@ def check_form_field(
         # /DocTimeStamps added for LTA validation purposes shouldn't have
         # an appearance (as per the recommendation in ISO 32000-2, which we
         # enforce as a rigid rule here)
-        if sig_obj.raw_get('/Type') == '/DocTimeStamp' and not visible:
+        if (
+            '/Type' in sig_obj
+            and sig_obj.raw_get('/Type') == '/DocTimeStamp'
+            and not visible
+        ):
             sig_whitelist = ModificationLevel.LTA_UPDATES
             valid_when_locked = True
         else:
diff --git a/pyhanko_tests/data/pdf/minimal-signed-twice-no-sig-type.pdf b/pyhanko_tests/data/pdf/minimal-signed-twice-no-sig-type.pdf
new file mode 100644
index 00000000..4da46f54
Binary files /dev/null and b/pyhanko_tests/data/pdf/minimal-signed-twice-no-sig-type.pdf differ
diff --git a/pyhanko_tests/test_diff_analysis.py b/pyhanko_tests/test_diff_analysis.py
index 19581fe1..d8f94d6b 100644
--- a/pyhanko_tests/test_diff_analysis.py
+++ b/pyhanko_tests/test_diff_analysis.py
@@ -2656,3 +2656,15 @@ def test_cant_descend_into_non_container():
 
     with pytest.raises(PdfReadError, match='Anchor'):
         root_rel.descend('/Blah')
+
+
+def test_signature_without_type_is_form_filling():
+    fname = f"{PDF_DATA_DIR}/minimal-signed-twice-no-sig-type.pdf"
+    with open(fname, 'rb') as inf:
+        r = PdfFileReader(inf)
+        s = r.embedded_signatures[0]
+        s.compute_integrity_info(DEFAULT_DIFF_POLICY)
+        assert s.field_name == 'Sig1'
+        assert (
+            s.diff_result.modification_level == ModificationLevel.FORM_FILLING
+        )