From 51d5312005e6a5b98f0e91e8701ea563516bd634 Mon Sep 17 00:00:00 2001
From: vera-rubin <322284620+vera-rubin@users.noreply.github.com>
Date: Wed, 14 Oct 2026 18:55:10 +0000
Subject: [PATCH] Fix significant-digit rounding after fractional carry

---
 babel/numbers.py                     |  3 +++
 tests/test_numbers_format_decimal.py | 10 ++++++++++
 2 files changed, 13 insertions(+)

diff --git a/babel/numbers.py b/babel/numbers.py
index b782521e5..2e142b183 100644
--- a/babel/numbers.py
+++ b/babel/numbers.py
@@ -1587,6 +1587,9 @@ def _format_significant(self, value: decimal.Decimal, minimum: int, maximum: int
         exp = value.adjusted()
         scale = maximum - 1 - exp
         digits = str(value.scaleb(scale).quantize(decimal.Decimal(1)))
+        # Account for a carry that increases the number of digits.
+        if len(digits) > maximum:
+            exp += 1
         if scale <= 0:
             result = digits + '0' * -scale
         else:
diff --git a/tests/test_numbers_format_decimal.py b/tests/test_numbers_format_decimal.py
index 98660a5ff..d06e0cea7 100644
--- a/tests/test_numbers_format_decimal.py
+++ b/tests/test_numbers_format_decimal.py
@@ -65,6 +65,16 @@ def test_significant_digits():
     assert numbers.format_decimal(0.1, '@@', locale='en_US') == '0.10'
 
 
+def test_significant_digits_fractional_carry():
+    for value, expected in [
+        ('0.00994', '0.0099'),
+        ('0.00999', '0.010'),
+        ('0.0999', '0.10'),
+        ('0.000999', '0.0010'),
+    ]:
+        assert numbers.format_decimal(decimal.Decimal(value), '@@', locale='en_US') == expected
+
+
 def test_decimals():
     """Test significant digits patterns"""
     assert numbers.format_decimal(decimal.Decimal('1.2345'), '#.00', locale='en_US') == '1.23'