diff --git a/mysql-test/r/func_time.result b/mysql-test/r/func_time.result
index 01743e4a1dc..bbb506035dc 100644
--- a/mysql-test/r/func_time.result
+++ b/mysql-test/r/func_time.result
@@ -1387,4 +1387,10 @@ STR_TO_DATE(SPACE(2),'1')
 SET GLOBAL SQL_MODE='';
 DO  STR_TO_DATE((''), FROM_DAYS(@@GLOBAL.SQL_MODE));
 SET GLOBAL SQL_MODE=DEFAULT;
+#
+# Bug#11766087  59125: VALGRIND UNINITIALISED VALUE WARNING IN ULL2DEC, LONGLONG2DECIMAL
+#
+SELECT FORMAT(YEAR(STR_TO_DATE('',GET_FORMAT(TIME,''))),1);
+FORMAT(YEAR(STR_TO_DATE('',GET_FORMAT(TIME,''))),1)
+NULL
 End of 5.1 tests
diff --git a/mysql-test/t/func_time.test b/mysql-test/t/func_time.test
index 3f441c42d48..2c3d3849793 100644
--- a/mysql-test/t/func_time.test
+++ b/mysql-test/t/func_time.test
@@ -895,4 +895,10 @@ SET GLOBAL SQL_MODE='';
 DO  STR_TO_DATE((''), FROM_DAYS(@@GLOBAL.SQL_MODE));
 SET GLOBAL SQL_MODE=DEFAULT;
 
+--echo #
+--echo # Bug#11766087  59125: VALGRIND UNINITIALISED VALUE WARNING IN ULL2DEC, LONGLONG2DECIMAL
+--echo #
+
+SELECT FORMAT(YEAR(STR_TO_DATE('',GET_FORMAT(TIME,''))),1);
+
 --echo End of 5.1 tests
diff --git a/sql/item_func.cc b/sql/item_func.cc
index 79fa37bd372..595629b51be 100644
--- a/sql/item_func.cc
+++ b/sql/item_func.cc
@@ -482,7 +482,10 @@ bool Item_func::is_expensive_processor(uchar *arg)
 my_decimal *Item_func::val_decimal(my_decimal *decimal_value)
 {
   DBUG_ASSERT(fixed);
-  int2my_decimal(E_DEC_FATAL_ERROR, val_int(), unsigned_flag, decimal_value);
+  longlong nr= val_int();
+  if (null_value)
+    return 0; /* purecov: inspected */
+  int2my_decimal(E_DEC_FATAL_ERROR, nr, unsigned_flag, decimal_value);
   return decimal_value;
 }