diff --git a/Lib/argparse.py b/Lib/argparse.py
index adf8bdf16f1f5a..08a3155fd16afc 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -1405,7 +1405,7 @@ def __init__(self,
         self._defaults = {}
 
         # determines whether an "option" looks like a negative number
-        self._negative_number_matcher = _re.compile(r'^-\d+$|^-\d*\.\d+$')
+        self._negative_number_matcher = _re.compile(r'^-(?:\d+(?:_\d+)*(?:\.\d+(?:_\d+)*)?|\.\d+(?:_\d+)*)$')
 
         # whether or not there are any optionals that look like negative
         # numbers -- uses a list so it can be shared and edited
diff --git a/Lib/test/test_argparse.py b/Lib/test/test_argparse.py
index 42998d5c6ea06d..67f1064b0c3b18 100644
--- a/Lib/test/test_argparse.py
+++ b/Lib/test/test_argparse.py
@@ -2092,6 +2092,29 @@ class TestActionExtend(ParserTestCase):
         ('--foo f1 --foo f2 f3 f4', NS(foo=['f1', 'f2', 'f3', 'f4'])),
     ]
 
+
+class TestNegativeNumber(ParserTestCase):
+    """Test parsing negative numbers"""
+
+    argument_signatures = [
+        Sig('--int', type=int),
+        Sig('--float', type=float),
+    ]
+    failures = [
+        '--float -_.45',
+        '--float -1__000.0',
+        '--int -1__000',
+    ]
+    successes = [
+        ('--int -1000 --float -1000.0', NS(int=-1000, float=-1000.0)),
+        ('--int -1_000 --float -1_000.0', NS(int=-1000, float=-1000.0)),
+        ('--int -1_000_000 --float -1_000_000.0', NS(int=-1000000, float=-1000000.0)),
+        ('--float -1_000.0', NS(int=None, float=-1000.0)),
+        ('--float -1_000_000.0_0', NS(int=None, float=-1000000.0)),
+        ('--float -.5', NS(int=None, float=-0.5)),
+        ('--float -.5_000', NS(int=None, float=-0.5)),
+    ]
+
 # ================
 # Subparsers tests
 # ================