From d29cd2fa8690eaf8c37da33ab6802e326442d794 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?S=C3=A9bastien=20Eustace?= <sebastien@eustace.io>
Date: Sat, 18 Feb 2017 14:02:51 -0500
Subject: [PATCH] Fixes precise_diff on full month.

---
 pendulum/helpers.py   | 14 ++++++++++----
 tests/test_helpers.py |  9 +++++++++
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/pendulum/helpers.py b/pendulum/helpers.py
index 2b890487..5f2a3029 100644
--- a/pendulum/helpers.py
+++ b/pendulum/helpers.py
@@ -190,11 +190,17 @@ def precise_diff(d1, d2):
                 d_diff += d1.day
             else:
                 d_diff += days_in_last_month
-
-            m_diff -= 1
-        else:
-            # We have a full month, remove days
+        elif d_diff == days_in_month - days_in_last_month:
+            # We have exactly a full month
+            # We remove the days difference
+            # and add one to the months difference
             d_diff = 0
+            m_diff += 1
+        else:
+            # We have a full month
+            d_diff += days_in_last_month
+
+        m_diff -= 1
 
     if m_diff < 0:
         m_diff += 12
diff --git a/tests/test_helpers.py b/tests/test_helpers.py
index c0775e8b..65c536e2 100644
--- a/tests/test_helpers.py
+++ b/tests/test_helpers.py
@@ -37,6 +37,15 @@ def test_precise_diff(self):
             hours=20, minutes=54, seconds=47, microseconds=282310
         )
 
+        dt1 = datetime(2017, 2, 17, 16, 5, 45, 123456)
+        dt2 = datetime(2018, 2, 17, 16, 5, 45, 123256)
+
+        diff = precise_diff(dt1, dt2)
+        self.assert_diff(
+            diff,
+            months=11, days=30, hours=23, minutes=59, seconds=59, microseconds=999800
+        )
+
     def assert_diff(self, diff,
                     years=0, months=0, days=0,
                     hours=0, minutes=0, seconds=0, microseconds=0):