diff --git a/types/convert.go b/types/convert.go
index ca59c6620b095..c86b342108704 100644
--- a/types/convert.go
+++ b/types/convert.go
@@ -369,23 +369,30 @@ func getValidIntPrefix(sc *stmtctx.StatementContext, str string) (string, error)
 	return floatStrToIntStr(sc, floatPrefix, str)
 }
 
-// roundIntStr is to round int string base on the number following dot.
+// roundIntStr is to round a **valid int string** base on the number following dot.
 func roundIntStr(numNextDot byte, intStr string) string {
 	if numNextDot < '5' {
 		return intStr
 	}
 	retStr := []byte(intStr)
-	for i := len(intStr) - 1; i >= 0; i-- {
-		if retStr[i] != '9' {
-			retStr[i]++
+	idx := len(intStr) - 1
+	for ; idx >= 1; idx-- {
+		if retStr[idx] != '9' {
+			retStr[idx]++
 			break
 		}
-		if i == 0 {
-			retStr[i] = '1'
+		retStr[idx] = '0'
+	}
+	if idx == 0 {
+		if intStr[0] == '9' {
+			retStr[0] = '1'
+			retStr = append(retStr, '0')
+		} else if isDigit(intStr[0]) {
+			retStr[0]++
+		} else {
+			retStr[1] = '1'
 			retStr = append(retStr, '0')
-			break
 		}
-		retStr[i] = '0'
 	}
 	return string(retStr)
 }
@@ -429,6 +436,7 @@ func floatStrToIntStr(sc *stmtctx.StatementContext, validFloat string, oriStr st
 		}
 		return intStr, nil
 	}
+	// intCnt and digits contain the prefix `+/-` if validFloat[0] is `+/-`
 	var intCnt int
 	digits := make([]byte, 0, len(validFloat))
 	if dotIdx == -1 {
@@ -451,7 +459,7 @@ func floatStrToIntStr(sc *stmtctx.StatementContext, validFloat string, oriStr st
 	intCnt += exp
 	if intCnt <= 0 {
 		intStr = "0"
-		if intCnt == 0 && len(digits) > 0 {
+		if intCnt == 0 && len(digits) > 0 && isDigit(digits[0]) {
 			intStr = roundIntStr(digits[0], intStr)
 		}
 		return intStr, nil
diff --git a/types/convert_test.go b/types/convert_test.go
index 01015cfdeb407..a14371b88e7a5 100644
--- a/types/convert_test.go
+++ b/types/convert_test.go
@@ -666,6 +666,21 @@ func (s *testTypeConvertSuite) TestConvert(c *C) {
 	signedAccept(c, mysql.TypeNewDecimal, dec, "-0.00123")
 }
 
+func (s *testTypeConvertSuite) TestRoundIntStr(c *C) {
+	cases := []struct {
+		a string
+		b byte
+		c string
+	}{
+		{"+999", '5', "+1000"},
+		{"999", '5', "1000"},
+		{"-999", '5', "-1000"},
+	}
+	for _, cc := range cases {
+		c.Assert(roundIntStr(cc.b, cc.a), Equals, cc.c)
+	}
+}
+
 func (s *testTypeConvertSuite) TestGetValidFloat(c *C) {
 	tests := []struct {
 		origin string
@@ -693,15 +708,31 @@ func (s *testTypeConvertSuite) TestGetValidFloat(c *C) {
 		_, err := strconv.ParseFloat(prefix, 64)
 		c.Assert(err, IsNil)
 	}
-	floatStr, err := floatStrToIntStr(sc, "1e9223372036854775807", "1e9223372036854775807")
-	c.Assert(err, IsNil)
-	c.Assert(floatStr, Equals, "1")
-	floatStr, err = floatStrToIntStr(sc, "125e342", "125e342.83")
-	c.Assert(err, IsNil)
-	c.Assert(floatStr, Equals, "125")
-	floatStr, err = floatStrToIntStr(sc, "1e21", "1e21")
-	c.Assert(err, IsNil)
-	c.Assert(floatStr, Equals, "1")
+
+	tests2 := []struct {
+		origin   string
+		expected string
+	}{
+		{"1e9223372036854775807", "1"},
+		{"125e342", "125"},
+		{"1e21", "1"},
+		{"1e5", "100000"},
+		{"-123.45678e5", "-12345678"},
+		{"+0.5", "1"},
+		{"-0.5", "-1"},
+		{".5e0", "1"},
+		{"+.5e0", "+1"},
+		{"-.5e0", "-1"},
+		{".5", "1"},
+		{"123.456789e5", "12345679"},
+		{"123.456784e5", "12345678"},
+		{"+999.9999e2", "+100000"},
+	}
+	for _, t := range tests2 {
+		str, err := floatStrToIntStr(sc, t.origin, t.origin)
+		c.Assert(err, IsNil)
+		c.Assert(str, Equals, t.expected, Commentf("%v, %v", t.origin, t.expected))
+	}
 }
 
 // TestConvertTime tests time related conversion.