diff --git a/expression/builtin_time_test.go b/expression/builtin_time_test.go
index 9bf8cc788e94e..0025aaf5ff394 100644
--- a/expression/builtin_time_test.go
+++ b/expression/builtin_time_test.go
@@ -1257,6 +1257,9 @@ func (s *testEvaluatorSuite) TestStrToDate(c *C) {
 		Success bool
 		Expect  time.Time
 	}{
+		{"10/28/2011 9:46:29 pm", "%m/%d/%Y %l:%i:%s %p", true, time.Date(2011, 10, 28, 21, 46, 29, 0, time.Local)},
+		{"10/28/2011 9:46:29 Pm", "%m/%d/%Y %l:%i:%s %p", true, time.Date(2011, 10, 28, 21, 46, 29, 0, time.Local)},
+		{"2011/10/28 9:46:29 am", "%Y/%m/%d %l:%i:%s %p", true, time.Date(2011, 10, 28, 9, 46, 29, 0, time.Local)},
 		{"20161122165022", `%Y%m%d%H%i%s`, true, time.Date(2016, 11, 22, 16, 50, 22, 0, time.Local)},
 		{"2016 11 22 16 50 22", `%Y%m%d%H%i%s`, true, time.Date(2016, 11, 22, 16, 50, 22, 0, time.Local)},
 		{"16-50-22 2016 11 22", `%H-%i-%s%Y%m%d`, true, time.Date(2016, 11, 22, 16, 50, 22, 0, time.Local)},
diff --git a/types/time.go b/types/time.go
index ca7ec7c158f87..341137cb82e13 100644
--- a/types/time.go
+++ b/types/time.go
@@ -2355,11 +2355,17 @@ const (
 )
 
 func isAMOrPM(t *MysqlTime, input string, ctx map[string]int) (string, bool) {
-	if strings.HasPrefix(input, "AM") {
+	if len(input) < 2 {
+		return input, false
+	}
+
+	s := strings.ToLower(input[:2])
+	switch s {
+	case "am":
 		ctx["%p"] = constForAM
-	} else if strings.HasPrefix(input, "PM") {
+	case "pm":
 		ctx["%p"] = constForPM
-	} else {
+	default:
 		return input, false
 	}
 	return input[2:], true