diff --git a/expression/builtin_math.go b/expression/builtin_math.go
index 4d30548c06a4a..41d976ee3df11 100644
--- a/expression/builtin_math.go
+++ b/expression/builtin_math.go
@@ -1142,6 +1142,7 @@ func (c *convFunctionClass) getFunction(ctx sessionctx.Context, args []Expressio
 	if err != nil {
 		return nil, err
 	}
+	bf.tp.Charset, bf.tp.Collate = ctx.GetSessionVars().GetCharsetInfo()
 	bf.tp.Flen = 64
 	sig := &builtinConvSig{bf}
 	sig.setPbCode(tipb.ScalarFuncSig_Conv)
diff --git a/expression/collation.go b/expression/collation.go
index 9c7f7345eb7c7..4163c670513fd 100644
--- a/expression/collation.go
+++ b/expression/collation.go
@@ -151,7 +151,7 @@ func deriveCoercibilityForScarlarFunc(sf *ScalarFunction) Coercibility {
 	if sf.RetType.EvalType() != types.ETString {
 		return CoercibilityNumeric
 	}
-	coer := CoercibilityIgnorable
+	coer := CoercibilityCoercible
 	for _, arg := range sf.GetArgs() {
 		if arg.Coercibility() < coer {
 			coer = arg.Coercibility()
@@ -178,7 +178,7 @@ func deriveCoercibilityForColumn(c *Column) Coercibility {
 
 // DeriveCollationFromExprs derives collation information from these expressions.
 func DeriveCollationFromExprs(ctx sessionctx.Context, exprs ...Expression) (dstCharset, dstCollation string) {
-	curCoer := CoercibilityCoercible
+	curCoer := CoercibilityIgnorable
 	curCollationPriority := -1
 	dstCharset, dstCollation = charset.GetDefaultCharsetAndCollate()
 	if ctx != nil && ctx.GetSessionVars() != nil {
diff --git a/expression/integration_test.go b/expression/integration_test.go
index ce8c0f58e8ecc..a55e2c2e567a1 100755
--- a/expression/integration_test.go
+++ b/expression/integration_test.go
@@ -7668,3 +7668,13 @@ func (s *testIntegrationSuite) TestIssue11333(c *C) {
 	tk.MustQuery(`select 0.0000000000000000000000000000000000000000000000000000000000000000000000012;`).Check(testkit.Rows("0.000000000000000000000000000000000000000000000000000000000000000000000001"))
 	tk.MustQuery(`select 0.000000000000000000000000000000000000000000000000000000000000000000000001;`).Check(testkit.Rows("0.000000000000000000000000000000000000000000000000000000000000000000000001"))
 }
+
+func (s *testIntegrationSerialSuite) TestIssue19116(c *C) {
+	collate.SetNewCollationEnabledForTest(true)
+	defer collate.SetNewCollationEnabledForTest(false)
+
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustQuery("select collation(concat(NULL,NULL));").Check(testkit.Rows("binary"))
+	tk.MustQuery("select coercibility(concat(1,1));").Check(testkit.Rows("4"))
+	tk.MustQuery("select coercibility(1);").Check(testkit.Rows("5"))
+}