diff --git a/pkg/expr/classic/reduce.go b/pkg/expr/classic/reduce.go
index 3fd74b6b4d8..28d85bd5d85 100644
--- a/pkg/expr/classic/reduce.go
+++ b/pkg/expr/classic/reduce.go
@@ -15,7 +15,7 @@ func (cr classicReducer) ValidReduceFunc() bool {
 	switch cr {
 	case "avg", "sum", "min", "max", "count", "last", "median":
 		return true
-	case "diff", "diff_abs", "percent_diff", "percent_diff_abs", "count_not_null":
+	case "diff", "diff_abs", "percent_diff", "percent_diff_abs", "count_non_null":
 		return true
 	}
 	return false
diff --git a/pkg/expr/classic/reduce_test.go b/pkg/expr/classic/reduce_test.go
index f4a5a39c37c..c30d33966d0 100644
--- a/pkg/expr/classic/reduce_test.go
+++ b/pkg/expr/classic/reduce_test.go
@@ -112,6 +112,7 @@ func TestReducer(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
+			require.Equal(t, true, tt.reducer.ValidReduceFunc())
 			num := tt.reducer.Reduce(tt.inputSeries)
 			require.Equal(t, tt.expectedNumber, num)
 		})