diff --git a/src/cmd/compile/internal/noder/irgen.go b/src/cmd/compile/internal/noder/irgen.go
index 3f362e9d2b..b70d82d7e6 100644
--- a/src/cmd/compile/internal/noder/irgen.go
+++ b/src/cmd/compile/internal/noder/irgen.go
@@ -38,6 +38,7 @@ func checkFiles(noders []*noder, importer types2.Importer) (posMap, *types2.Pack
 		GoVersion:             base.Flag.Lang,
 		IgnoreLabels:          true, // parser already checked via syntax.CheckBranches mode
 		CompilerErrorMessages: true, // use error strings matching existing compiler errors
+		AllowTypeLists:        true, // remove this line once all tests use type set syntax
 		Error: func(err error) {
 			terr := err.(types2.Error)
 			base.ErrorfAt(m.makeXPos(terr.Pos), "%s", terr.Msg)
diff --git a/src/cmd/compile/internal/types2/api.go b/src/cmd/compile/internal/types2/api.go
index 2939dcc0bd..433250f02c 100644
--- a/src/cmd/compile/internal/types2/api.go
+++ b/src/cmd/compile/internal/types2/api.go
@@ -125,6 +125,12 @@ type Config struct {
 	// TODO(gri) Consolidate error messages and remove this flag.
 	CompilerErrorMessages bool
 
+	// If AllowTypeLists is set, the type list syntax is permitted
+	// in an interface in addition to the type set syntax.
+	// TODO(gri) Remove once type lists are no longer supported by
+	//           the parser.
+	AllowTypeLists bool
+
 	// If go115UsesCgo is set, the type checker expects the
 	// _cgo_gotypes.go file generated by running cmd/cgo to be
 	// provided as a package source file. Qualified identifiers
diff --git a/src/cmd/compile/internal/types2/api_test.go b/src/cmd/compile/internal/types2/api_test.go
index d82d29cad8..49d710067a 100644
--- a/src/cmd/compile/internal/types2/api_test.go
+++ b/src/cmd/compile/internal/types2/api_test.go
@@ -345,7 +345,7 @@ func TestTypesInfo(t *testing.T) {
 		{genericPkg + `g0; type t[P any] int; var x struct{ f t[int] }; var _ = x.f`, `x.f`, `generic_g0.t[int]`},
 
 		// issue 45096
-		{genericPkg + `issue45096; func _[T interface{ type int8, int16, int32  }](x T) { _ = x < 0 }`, `0`, `generic_issue45096.T₁`},
+		{genericPkg + `issue45096; func _[T interface{ ~int8 | ~int16 | ~int32 }](x T) { _ = x < 0 }`, `0`, `generic_issue45096.T₁`},
 	}
 
 	for _, test := range tests {
@@ -454,38 +454,38 @@ func TestInferredInfo(t *testing.T) {
 		// 	`func(float64)`,
 		// },
 
-		{genericPkg + `s1; func f[T any, P interface{type *T}](x T); func _(x string) { f(x) }`,
+		{genericPkg + `s1; func f[T any, P interface{~*T}](x T); func _(x string) { f(x) }`,
 			`f`,
 			[]string{`string`, `*string`},
 			`func(x string)`,
 		},
-		{genericPkg + `s2; func f[T any, P interface{type *T}](x []T); func _(x []int) { f(x) }`,
+		{genericPkg + `s2; func f[T any, P interface{~*T}](x []T); func _(x []int) { f(x) }`,
 			`f`,
 			[]string{`int`, `*int`},
 			`func(x []int)`,
 		},
-		{genericPkg + `s3; type C[T any] interface{type chan<- T}; func f[T any, P C[T]](x []T); func _(x []int) { f(x) }`,
+		{genericPkg + `s3; type C[T any] interface{~chan<- T}; func f[T any, P C[T]](x []T); func _(x []int) { f(x) }`,
 			`f`,
 			[]string{`int`, `chan<- int`},
 			`func(x []int)`,
 		},
-		{genericPkg + `s4; type C[T any] interface{type chan<- T}; func f[T any, P C[T], Q C[[]*P]](x []T); func _(x []int) { f(x) }`,
+		{genericPkg + `s4; type C[T any] interface{~chan<- T}; func f[T any, P C[T], Q C[[]*P]](x []T); func _(x []int) { f(x) }`,
 			`f`,
 			[]string{`int`, `chan<- int`, `chan<- []*chan<- int`},
 			`func(x []int)`,
 		},
 
-		{genericPkg + `t1; func f[T any, P interface{type *T}]() T; func _() { _ = f[string] }`,
+		{genericPkg + `t1; func f[T any, P interface{~*T}]() T; func _() { _ = f[string] }`,
 			`f`,
 			[]string{`string`, `*string`},
 			`func() string`,
 		},
-		{genericPkg + `t2; type C[T any] interface{type chan<- T}; func f[T any, P C[T]]() []T; func _() { _ = f[int] }`,
+		{genericPkg + `t2; type C[T any] interface{~chan<- T}; func f[T any, P C[T]]() []T; func _() { _ = f[int] }`,
 			`f`,
 			[]string{`int`, `chan<- int`},
 			`func() []int`,
 		},
-		{genericPkg + `t3; type C[T any] interface{type chan<- T}; func f[T any, P C[T], Q C[[]*P]]() []T; func _() { _ = f[int] }`,
+		{genericPkg + `t3; type C[T any] interface{~chan<- T}; func f[T any, P C[T], Q C[[]*P]]() []T; func _() { _ = f[int] }`,
 			`f`,
 			[]string{`int`, `chan<- int`, `chan<- []*chan<- int`},
 			`func() []int`,
diff --git a/src/cmd/compile/internal/types2/interface.go b/src/cmd/compile/internal/types2/interface.go
index 770b8ba5cc..c79026f00d 100644
--- a/src/cmd/compile/internal/types2/interface.go
+++ b/src/cmd/compile/internal/types2/interface.go
@@ -34,18 +34,25 @@ func (check *Checker) interfaceType(ityp *Interface, iface *syntax.InterfaceType
 			continue // ignore
 		}
 
+		// TODO(gri) Remove type list handling once the parser doesn't accept type lists anymore.
 		if name == "type" {
+			// Report an error for the first type list per interface
+			// if we don't allow type lists, but continue.
+			if !check.conf.AllowTypeLists && tlist == nil {
+				check.softErrorf(f.Name, "use generalized embedding syntax instead of a type list")
+			}
 			// For now, collect all type list entries as if it
 			// were a single union, where each union element is
 			// of the form ~T.
-			// TODO(gri) remove once we disallow type lists
 			op := new(syntax.Operation)
 			// We should also set the position (but there is no setter);
 			// we don't care because this code will eventually go away.
 			op.Op = syntax.Tilde
 			op.X = f.Type
 			tlist = append(tlist, op)
-			if tname != nil && tname != f.Name {
+			// Report an error if we have multiple type lists in an
+			// interface, but only if they are permitted in the first place.
+			if check.conf.AllowTypeLists && tname != nil && tname != f.Name {
 				check.error(f.Name, "cannot have multiple type lists in an interface")
 			}
 			tname = f.Name
diff --git a/src/cmd/compile/internal/types2/testdata/examples/constraints.go2 b/src/cmd/compile/internal/types2/testdata/examples/constraints.go2
index efefaa2a25..d9805fe694 100644
--- a/src/cmd/compile/internal/types2/testdata/examples/constraints.go2
+++ b/src/cmd/compile/internal/types2/testdata/examples/constraints.go2
@@ -6,6 +6,18 @@
 
 package p
 
+type (
+	// Type lists are processed as unions but an error is reported.
+	// TODO(gri) remove this once the parser doesn't accept type lists anymore.
+	_ interface{
+		type /* ERROR use generalized embedding syntax instead of a type list */ int
+	}
+	_ interface{
+		type /* ERROR use generalized embedding syntax instead of a type list */ int
+		type float32
+	}
+)
+
 type (
 	// Arbitrary types may be embedded like interfaces.
 	_ interface{int}
diff --git a/src/cmd/compile/internal/types2/typestring_test.go b/src/cmd/compile/internal/types2/typestring_test.go
index 8d0ca760bf..88103b81b1 100644
--- a/src/cmd/compile/internal/types2/typestring_test.go
+++ b/src/cmd/compile/internal/types2/typestring_test.go
@@ -91,7 +91,6 @@ var independentTestTypes = []testEntry{
 	dup("interface{}"),
 	dup("interface{m()}"),
 	dup(`interface{String() string; m(int) float32}`),
-	{"interface{type int, float32, complex128}", "interface{~int|~float32|~complex128}"},
 	dup("interface{int|float32|complex128}"),
 	dup("interface{int|~float32|~complex128}"),