diff --git a/nvchecker/__init__.py b/nvchecker/__init__.py
index 471fec2..621fa57 100644
--- a/nvchecker/__init__.py
+++ b/nvchecker/__init__.py
@@ -1,4 +1,4 @@
 # MIT licensed
 # Copyright (c) 2013-2021 lilydjwg <lilydjwg@gmail.com>, et al.
 
-__version__ = '2.5'
+__version__ = '2.6dev'
diff --git a/nvchecker_source/regex.py b/nvchecker_source/regex.py
index 48406e1..551f78d 100644
--- a/nvchecker_source/regex.py
+++ b/nvchecker_source/regex.py
@@ -17,6 +17,8 @@ async def get_version_impl(info):
     regex = re.compile(conf['regex'])
   except sre_constants.error as e:
     raise GetVersionError('bad regex', exc_info=e)
+  if regex.groups > 1:
+    raise GetVersionError('multi-group regex')
 
   encoding = conf.get('encoding', 'latin1')
 
diff --git a/tests/test_regex.py b/tests/test_regex.py
index 1b4c255..bd04014 100644
--- a/tests/test_regex.py
+++ b/tests/test_regex.py
@@ -51,6 +51,14 @@ async def test_missing(get_version, httpbin):
           "regex": "foobar",
       })
 
+async def test_multi_group(get_version, httpbin):
+    with pytest.raises(RuntimeError):
+      await get_version("example", {
+          "source": "regex",
+          "url": httpbin.url + "/base64/" + base64_encode("1.2"),
+          "regex": r"(\d+)\.(\d+)",
+      })
+
 async def test_regex_with_tokenBasic(get_version, httpbin):
     assert await get_version("example", {
         "source": "regex",