diff --git a/mysql-test/r/func_group.result b/mysql-test/r/func_group.result
index e421da1c462..f245d272ede 100644
--- a/mysql-test/r/func_group.result
+++ b/mysql-test/r/func_group.result
@@ -1296,6 +1296,15 @@ select var_samp(e) as '0.5', var_pop(e) as '0.25' from bug22555;
 0.5	0.25
 0.5000	0.2500
 drop table bug22555;
+create table t1 (a decimal(20));
+insert into t1 values (12345678901234567890);
+select count(a) from t1;
+count(a)
+1
+select count(distinct a) from t1;
+count(distinct a)
+1
+drop table t1;
 CREATE TABLE t1 (a INT, b INT);
 INSERT INTO t1 VALUES (1,1),(1,2),(1,3),(1,4),(1,5),(1,6),(1,7),(1,8);
 INSERT INTO t1 SELECT a, b+8       FROM t1;
diff --git a/mysql-test/t/func_group.test b/mysql-test/t/func_group.test
index b102148472a..654bb8bb75d 100644
--- a/mysql-test/t/func_group.test
+++ b/mysql-test/t/func_group.test
@@ -793,6 +793,16 @@ select var_samp(e) as '0.5', var_pop(e) as '0.25' from bug22555;
 drop table bug22555;
 
 
+#
+# Bug #21976: Unnecessary warning with count(decimal)
+#
+
+create table t1 (a decimal(20));
+insert into t1 values (12345678901234567890);
+select count(a) from t1;
+select count(distinct a) from t1;
+drop table t1;
+
 #
 # Bug #23184: SELECT causes server crash
 # 
@@ -817,5 +827,4 @@ SELECT a,AVG(DISTINCT b) AS average FROM t1 GROUP BY a HAVING average > 50;
 
 DROP TABLE t1;
 
-###
 --echo End of 5.0 tests
diff --git a/sql/item.h b/sql/item.h
index 786d65ff6f4..1bded918741 100644
--- a/sql/item.h
+++ b/sql/item.h
@@ -694,12 +694,11 @@ public:
   virtual bool get_date_result(TIME *ltime,uint fuzzydate)
   { return get_date(ltime,fuzzydate); }
   /*
-    This function is used only in Item_func_isnull/Item_func_isnotnull
-    (implementations of IS NULL/IS NOT NULL clauses). Item_func_is{not}null
-    calls this method instead of one of val/result*() methods, which
-    normally will set null_value. This allows to determine nullness of
-    a complex expression without fully evaluating it.
-    Any new item which can be NULL must implement this call.
+    The method allows to determine nullness of a complex expression 
+    without fully evaluating it, instead of calling val/result*() then 
+    checking null_value. Used in Item_func_isnull/Item_func_isnotnull
+    and Item_sum_count/Item_sum_count_distinct.
+    Any new item which can be NULL must implement this method.
   */
   virtual bool is_null() { return 0; }
 
diff --git a/sql/item_sum.cc b/sql/item_sum.cc
index 41f0dd6496b..9c3c5f2053d 100644
--- a/sql/item_sum.cc
+++ b/sql/item_sum.cc
@@ -1050,14 +1050,8 @@ void Item_sum_count::clear()
 
 bool Item_sum_count::add()
 {
-  if (!args[0]->maybe_null)
+  if (!args[0]->maybe_null || !args[0]->is_null())
     count++;
-  else
-  {
-    args[0]->update_null_value();
-    if (!args[0]->null_value)
-      count++;
-  }
   return 0;
 }
 
@@ -1890,14 +1884,8 @@ void Item_sum_count::reset_field()
   char *res=result_field->ptr;
   longlong nr=0;
 
-  if (!args[0]->maybe_null)
+  if (!args[0]->maybe_null || !args[0]->is_null())
     nr=1;
-  else
-  {
-    args[0]->update_null_value();
-    if (!args[0]->null_value)
-      nr=1;
-  }
   int8store(res,nr);
 }
 
@@ -2000,14 +1988,8 @@ void Item_sum_count::update_field()
   char *res=result_field->ptr;
 
   nr=sint8korr(res);
-  if (!args[0]->maybe_null)
+  if (!args[0]->maybe_null || !args[0]->is_null())
     nr++;
-  else
-  {
-    args[0]->update_null_value();
-    if (!args[0]->null_value)
-      nr++;
-  }
   int8store(res,nr);
 }
 
@@ -2431,12 +2413,8 @@ bool Item_sum_count_distinct::setup(THD *thd)
     Item *item=args[i];
     if (list.push_back(item))
       return TRUE;                              // End of memory
-    if (item->const_item())
-    {
-      item->update_null_value();
-      if (item->null_value)
-	always_null=1;
-    }
+    if (item->const_item() && item->is_null())
+      always_null= 1;
   }
   if (always_null)
     return FALSE;