diff --git a/src/cmd/compile/internal/types2/typeset.go b/src/cmd/compile/internal/types2/typeset.go
index 8d33597ffd90a..14039ac9d6184 100644
--- a/src/cmd/compile/internal/types2/typeset.go
+++ b/src/cmd/compile/internal/types2/typeset.go
@@ -255,9 +255,8 @@ func computeInterfaceTypeSet(check *Checker, pos syntax.Pos, ityp *Interface) *_
 	allTerms := allTermlist
 	allComparable := false
 	for i, typ := range ityp.embeddeds {
-		// The embedding position is nil for imported interfaces
-		// and also for interface copies after substitution (but
-		// in that case we don't need to report errors again).
+		// The embedding position is nil for imported interfaces.
+		// We don't need to do version checks in those cases.
 		var pos syntax.Pos // embedding position
 		if ityp.embedPos != nil {
 			pos = (*ityp.embedPos)[i]
@@ -270,7 +269,7 @@ func computeInterfaceTypeSet(check *Checker, pos syntax.Pos, ityp *Interface) *_
 			assert(!isTypeParam(typ))
 			tset := computeInterfaceTypeSet(check, pos, u)
 			// If typ is local, an error was already reported where typ is specified/defined.
-			if check != nil && check.isImportedConstraint(typ) && !check.verifyVersionf(pos, go1_18, "embedding constraint interface %s", typ) {
+			if pos.IsKnown() && check != nil && check.isImportedConstraint(typ) && !check.verifyVersionf(pos, go1_18, "embedding constraint interface %s", typ) {
 				continue
 			}
 			comparable = tset.comparable
@@ -279,7 +278,7 @@ func computeInterfaceTypeSet(check *Checker, pos syntax.Pos, ityp *Interface) *_
 			}
 			terms = tset.terms
 		case *Union:
-			if check != nil && !check.verifyVersionf(pos, go1_18, "embedding interface element %s", u) {
+			if pos.IsKnown() && check != nil && !check.verifyVersionf(pos, go1_18, "embedding interface element %s", u) {
 				continue
 			}
 			tset := computeUnionTypeSet(check, unionSets, pos, u)
@@ -293,7 +292,7 @@ func computeInterfaceTypeSet(check *Checker, pos syntax.Pos, ityp *Interface) *_
 			if u == Typ[Invalid] {
 				continue
 			}
-			if check != nil && !check.verifyVersionf(pos, go1_18, "embedding non-interface type %s", typ) {
+			if pos.IsKnown() && check != nil && !check.verifyVersionf(pos, go1_18, "embedding non-interface type %s", typ) {
 				continue
 			}
 			terms = termlist{{false, typ}}
diff --git a/src/go/types/typeset.go b/src/go/types/typeset.go
index 4cd118a226553..a7d4485d0ef72 100644
--- a/src/go/types/typeset.go
+++ b/src/go/types/typeset.go
@@ -253,9 +253,8 @@ func computeInterfaceTypeSet(check *Checker, pos token.Pos, ityp *Interface) *_T
 	allTerms := allTermlist
 	allComparable := false
 	for i, typ := range ityp.embeddeds {
-		// The embedding position is nil for imported interfaces
-		// and also for interface copies after substitution (but
-		// in that case we don't need to report errors again).
+		// The embedding position is nil for imported interfaces.
+		// We don't need to do version checks in those cases.
 		var pos token.Pos // embedding position
 		if ityp.embedPos != nil {
 			pos = (*ityp.embedPos)[i]
@@ -268,7 +267,7 @@ func computeInterfaceTypeSet(check *Checker, pos token.Pos, ityp *Interface) *_T
 			assert(!isTypeParam(typ))
 			tset := computeInterfaceTypeSet(check, pos, u)
 			// If typ is local, an error was already reported where typ is specified/defined.
-			if check != nil && check.isImportedConstraint(typ) && !check.verifyVersionf(atPos(pos), go1_18, "embedding constraint interface %s", typ) {
+			if pos.IsValid() && check != nil && check.isImportedConstraint(typ) && !check.verifyVersionf(atPos(pos), go1_18, "embedding constraint interface %s", typ) {
 				continue
 			}
 			comparable = tset.comparable
@@ -277,7 +276,7 @@ func computeInterfaceTypeSet(check *Checker, pos token.Pos, ityp *Interface) *_T
 			}
 			terms = tset.terms
 		case *Union:
-			if check != nil && !check.verifyVersionf(atPos(pos), go1_18, "embedding interface element %s", u) {
+			if pos.IsValid() && check != nil && !check.verifyVersionf(atPos(pos), go1_18, "embedding interface element %s", u) {
 				continue
 			}
 			tset := computeUnionTypeSet(check, unionSets, pos, u)
@@ -291,7 +290,7 @@ func computeInterfaceTypeSet(check *Checker, pos token.Pos, ityp *Interface) *_T
 			if u == Typ[Invalid] {
 				continue
 			}
-			if check != nil && !check.verifyVersionf(atPos(pos), go1_18, "embedding non-interface type %s", typ) {
+			if pos.IsValid() && check != nil && !check.verifyVersionf(atPos(pos), go1_18, "embedding non-interface type %s", typ) {
 				continue
 			}
 			terms = termlist{{false, typ}}
diff --git a/src/internal/types/testdata/fixedbugs/issue66064.go b/src/internal/types/testdata/fixedbugs/issue66064.go
new file mode 100644
index 0000000000000..d4a361754be80
--- /dev/null
+++ b/src/internal/types/testdata/fixedbugs/issue66064.go
@@ -0,0 +1,15 @@
+// -lang=go1.16
+
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build go1.21
+
+package main
+
+import "slices"
+
+func main() {
+	_ = slices.Clone([]string{}) // no error should be reported here
+}