diff --git a/expression/builtin_control.go b/expression/builtin_control.go
index 80e8d5e233e14..58c83eb7a7cd8 100644
--- a/expression/builtin_control.go
+++ b/expression/builtin_control.go
@@ -169,11 +169,14 @@ func (c *caseWhenFunctionClass) getFunction(ctx sessionctx.Context, args []Expre
 	}
 	// Set retType to BINARY(0) if all arguments are of type NULL.
 	if fieldTp.Tp == mysql.TypeNull {
-		fieldTp.Flen, fieldTp.Decimal = 0, -1
+		fieldTp.Flen, fieldTp.Decimal = 0, types.UnspecifiedLength
 		types.SetBinChsClnFlag(fieldTp)
 	}
 	argTps := make([]types.EvalType, 0, l)
 	for i := 0; i < l-1; i += 2 {
+		if args[i], err = wrapWithIsTrue(ctx, true, args[i]); err != nil {
+			return nil, err
+		}
 		argTps = append(argTps, types.ETInt, tp)
 	}
 	if l%2 == 1 {
@@ -221,7 +224,7 @@ func (b *builtinCaseWhenIntSig) Clone() builtinFunc {
 }
 
 // evalInt evals a builtinCaseWhenIntSig.
-// See https://dev.mysql.com/doc/refman/5.7/en/case.html
+// See https://dev.mysql.com/doc/refman/5.7/en/control-flow-functions.html#operator_case
 func (b *builtinCaseWhenIntSig) evalInt(row chunk.Row) (ret int64, isNull bool, err error) {
 	var condition int64
 	args, l := b.getArgs(), len(b.getArgs())
@@ -257,7 +260,7 @@ func (b *builtinCaseWhenRealSig) Clone() builtinFunc {
 }
 
 // evalReal evals a builtinCaseWhenRealSig.
-// See https://dev.mysql.com/doc/refman/5.7/en/case.html
+// See https://dev.mysql.com/doc/refman/5.7/en/control-flow-functions.html#operator_case
 func (b *builtinCaseWhenRealSig) evalReal(row chunk.Row) (ret float64, isNull bool, err error) {
 	var condition int64
 	args, l := b.getArgs(), len(b.getArgs())
@@ -293,7 +296,7 @@ func (b *builtinCaseWhenDecimalSig) Clone() builtinFunc {
 }
 
 // evalDecimal evals a builtinCaseWhenDecimalSig.
-// See https://dev.mysql.com/doc/refman/5.7/en/case.html
+// See https://dev.mysql.com/doc/refman/5.7/en/control-flow-functions.html#operator_case
 func (b *builtinCaseWhenDecimalSig) evalDecimal(row chunk.Row) (ret *types.MyDecimal, isNull bool, err error) {
 	var condition int64
 	args, l := b.getArgs(), len(b.getArgs())
@@ -329,7 +332,7 @@ func (b *builtinCaseWhenStringSig) Clone() builtinFunc {
 }
 
 // evalString evals a builtinCaseWhenStringSig.
-// See https://dev.mysql.com/doc/refman/5.7/en/case.html
+// See https://dev.mysql.com/doc/refman/5.7/en/control-flow-functions.html#operator_case
 func (b *builtinCaseWhenStringSig) evalString(row chunk.Row) (ret string, isNull bool, err error) {
 	var condition int64
 	args, l := b.getArgs(), len(b.getArgs())
@@ -365,7 +368,7 @@ func (b *builtinCaseWhenTimeSig) Clone() builtinFunc {
 }
 
 // evalTime evals a builtinCaseWhenTimeSig.
-// See https://dev.mysql.com/doc/refman/5.7/en/case.html
+// See https://dev.mysql.com/doc/refman/5.7/en/control-flow-functions.html#operator_case
 func (b *builtinCaseWhenTimeSig) evalTime(row chunk.Row) (ret types.Time, isNull bool, err error) {
 	var condition int64
 	args, l := b.getArgs(), len(b.getArgs())
@@ -401,7 +404,7 @@ func (b *builtinCaseWhenDurationSig) Clone() builtinFunc {
 }
 
 // evalDuration evals a builtinCaseWhenDurationSig.
-// See https://dev.mysql.com/doc/refman/5.7/en/case.html
+// See https://dev.mysql.com/doc/refman/5.7/en/control-flow-functions.html#operator_case
 func (b *builtinCaseWhenDurationSig) evalDuration(row chunk.Row) (ret types.Duration, isNull bool, err error) {
 	var condition int64
 	args, l := b.getArgs(), len(b.getArgs())
@@ -437,7 +440,7 @@ func (b *builtinCaseWhenJSONSig) Clone() builtinFunc {
 }
 
 // evalJSON evals a builtinCaseWhenJSONSig.
-// See https://dev.mysql.com/doc/refman/5.7/en/case.html
+// See https://dev.mysql.com/doc/refman/5.7/en/control-flow-functions.html#operator_case
 func (b *builtinCaseWhenJSONSig) evalJSON(row chunk.Row) (ret json.BinaryJSON, isNull bool, err error) {
 	var condition int64
 	args, l := b.getArgs(), len(b.getArgs())
diff --git a/expression/builtin_control_test.go b/expression/builtin_control_test.go
index 23a59ebdc22b8..00a4aef065412 100644
--- a/expression/builtin_control_test.go
+++ b/expression/builtin_control_test.go
@@ -40,6 +40,8 @@ func (s *testEvaluatorSuite) TestCaseWhen(c *C) {
 		{[]interface{}{nil, 1, false, 2, 3}, 3},
 		{[]interface{}{1, jsonInt.GetMysqlJSON(), nil}, 3},
 		{[]interface{}{0, jsonInt.GetMysqlJSON(), nil}, nil},
+		{[]interface{}{0.1, 1, 2}, 1},
+		{[]interface{}{0.0, 1, 0.1, 2}, 2},
 	}
 	fc := funcs[ast.Case]
 	for _, t := range tbl {