4 files changed, 8 insertions, 3 deletions
diff --git a/src/go/types/builtins.go b/src/go/types/builtins.go
index afe5f5d0fc..05e032423c 100644
--- a/src/go/types/builtins.go
+++ b/src/go/types/builtins.go
@@ -174,7 +174,7 @@ func (check *Checker) builtin(x *operand, call *ast.CallExpr, id builtinId) (_ b
 			}
 		}
 
-		if mode == invalid {
+		if mode == invalid && typ != Typ[Invalid] {
 			check.invalidArg(x.pos(), "%s for %s", x, bin.name)
 			return
 		}
diff --git a/src/go/types/expr.go b/src/go/types/expr.go
index 0a2a811bd8..3f3c4f83c6 100644
--- a/src/go/types/expr.go
+++ b/src/go/types/expr.go
@@ -1064,7 +1064,7 @@ func (check *Checker) exprInternal(x *operand, e ast.Expr, hint Type) exprKind {
 					break
 				}
 			}
-			typ = check.typ(e.Type)
+			typ = check.typExpr(e.Type, nil, nil)
 			base = typ
 
 		case hint != nil:
diff --git a/src/go/types/testdata/cycles.src b/src/go/types/testdata/cycles.src
index 79e75e9316..59f112dba1 100644
--- a/src/go/types/testdata/cycles.src
+++ b/src/go/types/testdata/cycles.src
@@ -147,7 +147,7 @@ type (
 // test cases for issue 18643
 // (type cycle detection when non-type expressions are involved)
 type (
-	T14 [len(T14 /* ERROR cycle */ {})]int
+	T14 /* ERROR cycle */ [len(T14{})]int
 	T15 [][len(T15 /* ERROR cycle */ {})]int
 	T16 map[[len(T16 /* ERROR cycle */ {1:2})]int]int
 	T17 map[int][len(T17 /* ERROR cycle */ {1:2})]int
diff --git a/src/go/types/typexpr.go b/src/go/types/typexpr.go
index e3f50000ec..45ada5874b 100644
--- a/src/go/types/typexpr.go
+++ b/src/go/types/typexpr.go
@@ -161,6 +161,11 @@ func (check *Checker) typExpr(e ast.Expr, def *Named, path []*TypeName) (T Type)
 	return
 }
 
+// typ is like typExpr (with a nil argument for the def parameter),
+// but typ breaks type cycles. It should be called for components of
+// types that break cycles, such as pointer base types, slice or map
+// element types, etc. See the comment in typExpr for details.
+//
 func (check *Checker) typ(e ast.Expr) Type {
 	// typExpr is called with a nil path indicating an indirection:
 	// push indir sentinel on object path