diff --git a/src/go/types/check_test.go b/src/go/types/check_test.go
index 6c3b630a1b..5a3e57ba44 100644
--- a/src/go/types/check_test.go
+++ b/src/go/types/check_test.go
@@ -207,12 +207,15 @@ func checkFiles(t *testing.T, sizes Sizes, goVersion string, filenames []string,
 		t.Fatal("no source files")
 	}
 
+	if strings.HasSuffix(filenames[0], ".go2") && !typeparams.Enabled {
+		t.Skip("type params are not enabled")
+	}
+	if strings.HasSuffix(filenames[0], ".go1") && typeparams.Enabled {
+		t.Skip("type params are enabled")
+	}
+
 	mode := parser.AllErrors
-	if strings.HasSuffix(filenames[0], ".go2") {
-		if !typeparams.Enabled {
-			t.Skip("type params are not enabled")
-		}
-	} else {
+	if !strings.HasSuffix(filenames[0], ".go2") {
 		mode |= typeparams.DisallowParsing
 	}
 
diff --git a/src/go/types/testdata/fixedbugs/issue46404.go1 b/src/go/types/testdata/fixedbugs/issue46404.go1
new file mode 100644
index 0000000000..db604bc1ac
--- /dev/null
+++ b/src/go/types/testdata/fixedbugs/issue46404.go1
@@ -0,0 +1,8 @@
+// Copyright 2021 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.
+
+package issue46404
+
+// Check that we don't type check t[_] as an instantiation.
+type t [t /* ERROR not a type */ [_]]_ // ERROR cannot use
diff --git a/src/go/types/typexpr.go b/src/go/types/typexpr.go
index 5185c33fcb..1738d864a6 100644
--- a/src/go/types/typexpr.go
+++ b/src/go/types/typexpr.go
@@ -463,8 +463,12 @@ func (check *Checker) typInternal(e0 ast.Expr, def *Named) (T Type) {
 		}
 
 	case *ast.IndexExpr:
-		exprs := typeparams.UnpackExpr(e.Index)
-		return check.instantiatedType(e.X, exprs, def)
+		if typeparams.Enabled {
+			exprs := typeparams.UnpackExpr(e.Index)
+			return check.instantiatedType(e.X, exprs, def)
+		}
+		check.errorf(e0, _NotAType, "%s is not a type", e0)
+		check.use(e.X)
 
 	case *ast.ParenExpr:
 		// Generic types must be instantiated before they can be used in any form.