diff --git a/expression/aggregation/base_func.go b/expression/aggregation/base_func.go
index 352e1cc870a1b..17762632454c4 100644
--- a/expression/aggregation/base_func.go
+++ b/expression/aggregation/base_func.go
@@ -120,6 +120,7 @@ func (a *baseFuncDesc) typeInfer(ctx sessionctx.Context) error {
 func (a *baseFuncDesc) typeInfer4Count(ctx sessionctx.Context) {
 	a.RetTp = types.NewFieldType(mysql.TypeLonglong)
 	a.RetTp.Flen = 21
+	a.RetTp.Decimal = 0
 	types.SetBinChsClnFlag(a.RetTp)
 }
 
diff --git a/expression/typeinfer_test.go b/expression/typeinfer_test.go
index e53b98311bf6d..911ca01de79d6 100644
--- a/expression/typeinfer_test.go
+++ b/expression/typeinfer_test.go
@@ -835,6 +835,7 @@ func (s *testInferTypeSuite) createTestCase4Aggregations() []typeInferTestCase {
 		{"avg(1.2e2)", mysql.TypeDouble, charset.CharsetBin, mysql.BinaryFlag, mysql.MaxRealWidth, types.UnspecifiedLength},
 		{"avg(c_char)", mysql.TypeDouble, charset.CharsetBin, mysql.BinaryFlag, mysql.MaxRealWidth, types.UnspecifiedLength},
 		{"group_concat(c_int_d)", mysql.TypeVarString, charset.CharsetUTF8MB4, 0, mysql.MaxBlobWidth, 0},
+		{"count(c_decimal)", mysql.TypeLonglong, charset.CharsetBin, mysql.BinaryFlag, 21, 0},
 	}
 }