diff --git a/mysql-test/r/func_time.result b/mysql-test/r/func_time.result
index 66fe355ffce..699f0c9ec4b 100644
--- a/mysql-test/r/func_time.result
+++ b/mysql-test/r/func_time.result
@@ -667,6 +667,78 @@ timestampdiff(SQL_TSI_DAY, '1996-02-01', '1996-03-01') as a3,
 timestampdiff(SQL_TSI_DAY, '2000-02-01', '2000-03-01') as a4;
 a1	a2	a3	a4
 28	28	29	29
+SELECT TIMESTAMPDIFF(day,'2006-01-10 14:30:28','2006-01-11 14:30:27');
+TIMESTAMPDIFF(day,'2006-01-10 14:30:28','2006-01-11 14:30:27')
+0
+SELECT TIMESTAMPDIFF(day,'2006-01-10 14:30:28','2006-01-11 14:30:28');
+TIMESTAMPDIFF(day,'2006-01-10 14:30:28','2006-01-11 14:30:28')
+1
+SELECT TIMESTAMPDIFF(day,'2006-01-10 14:30:28','2006-01-11 14:30:29');
+TIMESTAMPDIFF(day,'2006-01-10 14:30:28','2006-01-11 14:30:29')
+1
+SELECT TIMESTAMPDIFF(day,'2006-01-10 14:30:28','2006-01-12 14:30:27');
+TIMESTAMPDIFF(day,'2006-01-10 14:30:28','2006-01-12 14:30:27')
+1
+SELECT TIMESTAMPDIFF(day,'2006-01-10 14:30:28','2006-01-12 14:30:28');
+TIMESTAMPDIFF(day,'2006-01-10 14:30:28','2006-01-12 14:30:28')
+2
+SELECT TIMESTAMPDIFF(day,'2006-01-10 14:30:28','2006-01-12 14:30:29');
+TIMESTAMPDIFF(day,'2006-01-10 14:30:28','2006-01-12 14:30:29')
+2
+SELECT TIMESTAMPDIFF(week,'2006-01-10 14:30:28','2006-01-17 14:30:27');
+TIMESTAMPDIFF(week,'2006-01-10 14:30:28','2006-01-17 14:30:27')
+0
+SELECT TIMESTAMPDIFF(week,'2006-01-10 14:30:28','2006-01-17 14:30:28');
+TIMESTAMPDIFF(week,'2006-01-10 14:30:28','2006-01-17 14:30:28')
+1
+SELECT TIMESTAMPDIFF(week,'2006-01-10 14:30:28','2006-01-17 14:30:29');
+TIMESTAMPDIFF(week,'2006-01-10 14:30:28','2006-01-17 14:30:29')
+1
+SELECT TIMESTAMPDIFF(week,'2006-01-10 14:30:28','2006-01-24 14:30:27');
+TIMESTAMPDIFF(week,'2006-01-10 14:30:28','2006-01-24 14:30:27')
+1
+SELECT TIMESTAMPDIFF(week,'2006-01-10 14:30:28','2006-01-24 14:30:28');
+TIMESTAMPDIFF(week,'2006-01-10 14:30:28','2006-01-24 14:30:28')
+2
+SELECT TIMESTAMPDIFF(week,'2006-01-10 14:30:28','2006-01-24 14:30:29');
+TIMESTAMPDIFF(week,'2006-01-10 14:30:28','2006-01-24 14:30:29')
+2
+SELECT TIMESTAMPDIFF(month,'2006-01-10 14:30:28','2006-02-10 14:30:27');
+TIMESTAMPDIFF(month,'2006-01-10 14:30:28','2006-02-10 14:30:27')
+0
+SELECT TIMESTAMPDIFF(month,'2006-01-10 14:30:28','2006-02-10 14:30:28');
+TIMESTAMPDIFF(month,'2006-01-10 14:30:28','2006-02-10 14:30:28')
+1
+SELECT TIMESTAMPDIFF(month,'2006-01-10 14:30:28','2006-02-10 14:30:29');
+TIMESTAMPDIFF(month,'2006-01-10 14:30:28','2006-02-10 14:30:29')
+1
+SELECT TIMESTAMPDIFF(month,'2006-01-10 14:30:28','2006-03-10 14:30:27');
+TIMESTAMPDIFF(month,'2006-01-10 14:30:28','2006-03-10 14:30:27')
+1
+SELECT TIMESTAMPDIFF(month,'2006-01-10 14:30:28','2006-03-10 14:30:28');
+TIMESTAMPDIFF(month,'2006-01-10 14:30:28','2006-03-10 14:30:28')
+2
+SELECT TIMESTAMPDIFF(month,'2006-01-10 14:30:28','2006-03-10 14:30:29');
+TIMESTAMPDIFF(month,'2006-01-10 14:30:28','2006-03-10 14:30:29')
+2
+SELECT TIMESTAMPDIFF(year,'2006-01-10 14:30:28','2007-01-10 14:30:27');
+TIMESTAMPDIFF(year,'2006-01-10 14:30:28','2007-01-10 14:30:27')
+0
+SELECT TIMESTAMPDIFF(year,'2006-01-10 14:30:28','2007-01-10 14:30:28');
+TIMESTAMPDIFF(year,'2006-01-10 14:30:28','2007-01-10 14:30:28')
+1
+SELECT TIMESTAMPDIFF(year,'2006-01-10 14:30:28','2007-01-10 14:30:29');
+TIMESTAMPDIFF(year,'2006-01-10 14:30:28','2007-01-10 14:30:29')
+1
+SELECT TIMESTAMPDIFF(year,'2006-01-10 14:30:28','2008-01-10 14:30:27');
+TIMESTAMPDIFF(year,'2006-01-10 14:30:28','2008-01-10 14:30:27')
+1
+SELECT TIMESTAMPDIFF(year,'2006-01-10 14:30:28','2008-01-10 14:30:28');
+TIMESTAMPDIFF(year,'2006-01-10 14:30:28','2008-01-10 14:30:28')
+2
+SELECT TIMESTAMPDIFF(year,'2006-01-10 14:30:28','2008-01-10 14:30:29');
+TIMESTAMPDIFF(year,'2006-01-10 14:30:28','2008-01-10 14:30:29')
+2
 select date_add(time,INTERVAL 1 SECOND) from t1;
 date_add(time,INTERVAL 1 SECOND)
 NULL
diff --git a/mysql-test/t/func_time.test b/mysql-test/t/func_time.test
index 188e5667009..83b877e725c 100644
--- a/mysql-test/t/func_time.test
+++ b/mysql-test/t/func_time.test
@@ -318,6 +318,37 @@ select timestampdiff(SQL_TSI_DAY, '1986-02-01', '1986-03-01') as a1,
        timestampdiff(SQL_TSI_DAY, '1996-02-01', '1996-03-01') as a3,
        timestampdiff(SQL_TSI_DAY, '2000-02-01', '2000-03-01') as a4;
 
+# bug 16226
+SELECT TIMESTAMPDIFF(day,'2006-01-10 14:30:28','2006-01-11 14:30:27');
+SELECT TIMESTAMPDIFF(day,'2006-01-10 14:30:28','2006-01-11 14:30:28');
+SELECT TIMESTAMPDIFF(day,'2006-01-10 14:30:28','2006-01-11 14:30:29');
+SELECT TIMESTAMPDIFF(day,'2006-01-10 14:30:28','2006-01-12 14:30:27');
+SELECT TIMESTAMPDIFF(day,'2006-01-10 14:30:28','2006-01-12 14:30:28');
+SELECT TIMESTAMPDIFF(day,'2006-01-10 14:30:28','2006-01-12 14:30:29');
+
+SELECT TIMESTAMPDIFF(week,'2006-01-10 14:30:28','2006-01-17 14:30:27');
+SELECT TIMESTAMPDIFF(week,'2006-01-10 14:30:28','2006-01-17 14:30:28');
+SELECT TIMESTAMPDIFF(week,'2006-01-10 14:30:28','2006-01-17 14:30:29');
+SELECT TIMESTAMPDIFF(week,'2006-01-10 14:30:28','2006-01-24 14:30:27');
+SELECT TIMESTAMPDIFF(week,'2006-01-10 14:30:28','2006-01-24 14:30:28');
+SELECT TIMESTAMPDIFF(week,'2006-01-10 14:30:28','2006-01-24 14:30:29');
+
+SELECT TIMESTAMPDIFF(month,'2006-01-10 14:30:28','2006-02-10 14:30:27');
+SELECT TIMESTAMPDIFF(month,'2006-01-10 14:30:28','2006-02-10 14:30:28');
+SELECT TIMESTAMPDIFF(month,'2006-01-10 14:30:28','2006-02-10 14:30:29');
+SELECT TIMESTAMPDIFF(month,'2006-01-10 14:30:28','2006-03-10 14:30:27');
+SELECT TIMESTAMPDIFF(month,'2006-01-10 14:30:28','2006-03-10 14:30:28');
+SELECT TIMESTAMPDIFF(month,'2006-01-10 14:30:28','2006-03-10 14:30:29');
+
+SELECT TIMESTAMPDIFF(year,'2006-01-10 14:30:28','2007-01-10 14:30:27');
+SELECT TIMESTAMPDIFF(year,'2006-01-10 14:30:28','2007-01-10 14:30:28');
+SELECT TIMESTAMPDIFF(year,'2006-01-10 14:30:28','2007-01-10 14:30:29');
+SELECT TIMESTAMPDIFF(year,'2006-01-10 14:30:28','2008-01-10 14:30:27');
+SELECT TIMESTAMPDIFF(year,'2006-01-10 14:30:28','2008-01-10 14:30:28');
+SELECT TIMESTAMPDIFF(year,'2006-01-10 14:30:28','2008-01-10 14:30:29');
+
+# end of bug
+
 select date_add(time,INTERVAL 1 SECOND) from t1;
 drop table t1;
 
diff --git a/sql/item_timefunc.cc b/sql/item_timefunc.cc
index 9e1962835c8..835be6554bc 100644
--- a/sql/item_timefunc.cc
+++ b/sql/item_timefunc.cc
@@ -2877,6 +2877,8 @@ longlong Item_func_timestamp_diff::val_int()
   {
     uint year_beg, year_end, month_beg, month_end, day_beg, day_end;
     uint years= 0;
+    uint second_beg, second_end, microsecond_beg, microsecond_end;
+
     if (neg == -1)
     {
       year_beg= ltime2.year;
@@ -2885,6 +2887,10 @@ longlong Item_func_timestamp_diff::val_int()
       month_end= ltime1.month;
       day_beg= ltime2.day;
       day_end= ltime1.day;
+      second_beg= ltime2.hour * 3600 + ltime2.minute * 60 + ltime2.second;
+      second_end= ltime1.hour * 3600 + ltime1.minute * 60 + ltime1.second;
+      microsecond_beg= ltime2.second_part;
+      microsecond_end= ltime1.second_part;
     }
     else
     {
@@ -2894,6 +2900,10 @@ longlong Item_func_timestamp_diff::val_int()
       month_end= ltime2.month;
       day_beg= ltime1.day;
       day_end= ltime2.day;
+      second_beg= ltime1.hour * 3600 + ltime1.minute * 60 + ltime1.second;
+      second_end= ltime2.hour * 3600 + ltime2.minute * 60 + ltime2.second;
+      microsecond_beg= ltime1.second_part;
+      microsecond_end= ltime2.second_part;
     }
 
     /* calc years */
@@ -2907,8 +2917,13 @@ longlong Item_func_timestamp_diff::val_int()
       months+= 12 - (month_beg - month_end);
     else
       months+= (month_end - month_beg);
+
     if (day_end < day_beg)
       months-= 1;
+    else if ((day_end == day_beg) &&
+	     ((second_end < second_beg) ||
+	      (second_end == second_beg && microsecond_end < microsecond_beg)))
+      months-= 1;
   }
 
   switch (int_type) {