diff --git a/expression/builtin_string.go b/expression/builtin_string.go
index 4998aa24885c8..100e78a2ac6d7 100644
--- a/expression/builtin_string.go
+++ b/expression/builtin_string.go
@@ -232,7 +232,7 @@ func (b *builtinASCIISig) Clone() builtinFunc {
 	return newSig
 }
 
-// eval evals a builtinASCIISig.
+// evalInt evals a builtinASCIISig.
 // See https://dev.mysql.com/doc/refman/5.7/en/string-functions.html#function_ascii
 func (b *builtinASCIISig) evalInt(row chunk.Row) (int64, bool, error) {
 	val, isNull, err := b.args[0].EvalString(b.ctx, row)
@@ -285,6 +285,7 @@ func (b *builtinConcatSig) Clone() builtinFunc {
 	return newSig
 }
 
+// evalString evals a builtinConcatSig
 // See https://dev.mysql.com/doc/refman/5.7/en/string-functions.html#function_concat
 func (b *builtinConcatSig) evalString(row chunk.Row) (d string, isNull bool, err error) {
 	var s []byte
@@ -568,7 +569,7 @@ func (b *builtinRepeatSig) Clone() builtinFunc {
 	return newSig
 }
 
-// eval evals a builtinRepeatSig.
+// evalString evals a builtinRepeatSig.
 // See https://dev.mysql.com/doc/refman/5.7/en/string-functions.html#function_repeat
 func (b *builtinRepeatSig) evalString(row chunk.Row) (d string, isNull bool, err error) {
 	str, isNull, err := b.args[0].EvalString(b.ctx, row)
@@ -1515,6 +1516,7 @@ type trimFunctionClass struct {
 	baseFunctionClass
 }
 
+// getFunction sets trim built-in function signature.
 // The syntax of trim in mysql is 'TRIM([{BOTH | LEADING | TRAILING} [remstr] FROM] str), TRIM([remstr FROM] str)',
 // but we wil convert it into trim(str), trim(str, remstr) and trim(str, remstr, direction) in AST.
 func (c *trimFunctionClass) getFunction(ctx sessionctx.Context, args []Expression) (builtinFunc, error) {
@@ -2482,8 +2484,8 @@ func (b *builtinOctStringSig) Clone() builtinFunc {
 	return newSig
 }
 
-// // evalString evals OCT(N).
-// // See https://dev.mysql.com/doc/refman/5.7/en/string-functions.html#function_oct
+// evalString evals OCT(N).
+// See https://dev.mysql.com/doc/refman/5.7/en/string-functions.html#function_oct
 func (b *builtinOctStringSig) evalString(row chunk.Row) (string, bool, error) {
 	val, isNull, err := b.args[0].EvalString(b.ctx, row)
 	if isNull || err != nil {
@@ -2999,17 +3001,26 @@ func (c *toBase64FunctionClass) getFunction(ctx sessionctx.Context, args []Expre
 	}
 	bf := newBaseBuiltinFuncWithTp(ctx, args, types.ETString, types.ETString)
 	bf.tp.Flen = base64NeededEncodedLength(bf.args[0].GetType().Flen)
-	sig := &builtinToBase64Sig{bf}
+
+	valStr, _ := ctx.GetSessionVars().GetSystemVar(variable.MaxAllowedPacket)
+	maxAllowedPacket, err := strconv.ParseUint(valStr, 10, 64)
+	if err != nil {
+		return nil, errors.Trace(err)
+	}
+
+	sig := &builtinToBase64Sig{bf, maxAllowedPacket}
 	return sig, nil
 }
 
 type builtinToBase64Sig struct {
 	baseBuiltinFunc
+	maxAllowedPacket uint64
 }
 
 func (b *builtinToBase64Sig) Clone() builtinFunc {
 	newSig := &builtinToBase64Sig{}
 	newSig.cloneFrom(&b.baseBuiltinFunc)
+	newSig.maxAllowedPacket = b.maxAllowedPacket
 	return newSig
 }
 
@@ -3043,7 +3054,14 @@ func (b *builtinToBase64Sig) evalString(row chunk.Row) (d string, isNull bool, e
 	if isNull || err != nil {
 		return "", isNull, errors.Trace(err)
 	}
-
+	needEncodeLen := base64NeededEncodedLength(len(str))
+	if needEncodeLen == -1 {
+		return "", true, nil
+	}
+	if needEncodeLen > int(b.maxAllowedPacket) {
+		b.ctx.GetSessionVars().StmtCtx.AppendWarning(errWarnAllowedPacketOverflowed.GenByArgs("to_base64", b.maxAllowedPacket))
+		return "", true, nil
+	}
 	if b.tp.Flen == -1 || b.tp.Flen > mysql.MaxBlobWidth {
 		return "", true, nil
 	}
diff --git a/expression/builtin_string_test.go b/expression/builtin_string_test.go
index 3d067da53a335..7341f7f1055dc 100644
--- a/expression/builtin_string_test.go
+++ b/expression/builtin_string_test.go
@@ -23,6 +23,7 @@ import (
 	. "github.com/pingcap/check"
 	"github.com/pingcap/tidb/ast"
 	"github.com/pingcap/tidb/mysql"
+	"github.com/pingcap/tidb/sessionctx/stmtctx"
 	"github.com/pingcap/tidb/terror"
 	"github.com/pingcap/tidb/types"
 	"github.com/pingcap/tidb/util/charset"
@@ -1879,6 +1880,74 @@ func (s *testEvaluatorSuite) TestToBase64(c *C) {
 	c.Assert(err, IsNil)
 }
 
+func (s *testEvaluatorSuite) TestToBase64Sig(c *C) {
+	colTypes := []*types.FieldType{
+		{Tp: mysql.TypeVarchar},
+	}
+
+	tests := []struct {
+		args           string
+		expect         string
+		isNil          bool
+		maxAllowPacket uint64
+	}{
+		{"abc", "YWJj", false, 4},
+		{"abc", "", true, 3},
+		{
+			"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/",
+			"QUJDREVGR0hJSktMTU5PUFFSU1RVVldYWVphYmNkZWZnaGlqa2xtbm9wcXJzdHV2d3h5ejAxMjM0\nNTY3ODkrLw==",
+			false,
+			89,
+		},
+		{
+			"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/",
+			"",
+			true,
+			88,
+		},
+		{
+			"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/",
+			"QUJDREVGR0hJSktMTU5PUFFSU1RVVldYWVphYmNkZWZnaGlqa2xtbm9wcXJzdHV2d3h5ejAxMjM0\nNTY3ODkrL0FCQ0RFRkdISUpLTE1OT1BRUlNUVVZXWFlaYWJjZGVmZ2hpamtsbW5vcHFyc3R1dnd4\neXowMTIzNDU2Nzg5Ky9BQkNERUZHSElKS0xNTk9QUVJTVFVWV1hZWmFiY2RlZmdoaWprbG1ub3Bx\ncnN0dXZ3eHl6MDEyMzQ1Njc4OSsv",
+			false,
+			259,
+		},
+		{
+			"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/",
+			"",
+			true,
+			258,
+		},
+	}
+
+	args := []Expression{
+		&Column{Index: 0, RetType: colTypes[0]},
+	}
+
+	for _, test := range tests {
+		resultType := &types.FieldType{Tp: mysql.TypeVarchar, Flen: base64NeededEncodedLength(len(test.args))}
+		base := baseBuiltinFunc{args: args, ctx: s.ctx, tp: resultType}
+		toBase64 := &builtinToBase64Sig{base, test.maxAllowPacket}
+
+		input := chunk.NewChunkWithCapacity(colTypes, 1)
+		input.AppendString(0, test.args)
+		res, isNull, err := toBase64.evalString(input.GetRow(0))
+		c.Assert(err, IsNil)
+		if test.isNil {
+			c.Assert(isNull, IsTrue)
+
+			warnings := s.ctx.GetSessionVars().StmtCtx.GetWarnings()
+			c.Assert(len(warnings), Equals, 1)
+			lastWarn := warnings[len(warnings)-1]
+			c.Assert(terror.ErrorEqual(errWarnAllowedPacketOverflowed, lastWarn.Err), IsTrue)
+			s.ctx.GetSessionVars().StmtCtx.SetWarnings([]stmtctx.SQLWarn{})
+
+		} else {
+			c.Assert(isNull, IsFalse)
+		}
+		c.Assert(res, Equals, test.expect)
+	}
+}
+
 func (s *testEvaluatorSuite) TestStringRight(c *C) {
 	defer testleak.AfterTest(c)()
 	fc := funcs[ast.Right]