diff --git a/promql/bench_test.go b/promql/bench_test.go
index 695b2c1eb4..773ba2acfb 100644
--- a/promql/bench_test.go
+++ b/promql/bench_test.go
@@ -660,6 +660,15 @@ func BenchmarkParser(b *testing.B) {
 			}
 		})
 	}
+	for _, c := range cases {
+		b.Run("preprocess "+c, func(b *testing.B) {
+			expr, _ := parser.ParseExpr(c)
+			start, end := time.Now().Add(-time.Hour), time.Now()
+			for i := 0; i < b.N; i++ {
+				promql.PreprocessExpr(expr, start, end)
+			}
+		})
+	}
 	for _, c := range errCases {
 		name := fmt.Sprintf("%s (should fail)", c)
 		b.Run(name, func(b *testing.B) {