diff --git a/plan9/mksyscall.go b/plan9/mksyscall.go
index c403de1..2d07e8b 100644
--- a/plan9/mksyscall.go
+++ b/plan9/mksyscall.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build ignore
 // +build ignore
 
 /*
@@ -49,7 +50,12 @@
 	return "go run mksyscall.go " + strings.Join(os.Args[1:], " ")
 }
 
-// buildTags returns build tags
+// goBuildTags returns build tags in the go:build format.
+func goBuildTags() string {
+	return strings.ReplaceAll(*tags, ",", " && ")
+}
+
+// plusBuildTags returns build tags in the +build format.
 func buildTags() string {
 	return *tags
 }
@@ -377,12 +383,13 @@
 		}
 		file.Close()
 	}
-	fmt.Printf(srcTemplate, cmdLine(), buildTags(), text)
+	fmt.Printf(srcTemplate, cmdLine(), goBuildTags(), plusBuildTags(), text)
 }
 
 const srcTemplate = `// %s
 // Code generated by the command above; see README.md. DO NOT EDIT.
 
+//go:build %s
 // +build %s
 
 package plan9
diff --git a/plan9/pwd_go15_plan9.go b/plan9/pwd_go15_plan9.go
index 87ae9d2..c9b6993 100644
--- a/plan9/pwd_go15_plan9.go
+++ b/plan9/pwd_go15_plan9.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build go1.5
 // +build go1.5
 
 package plan9
diff --git a/plan9/pwd_plan9.go b/plan9/pwd_plan9.go
index c07c798..98bf56b 100644
--- a/plan9/pwd_plan9.go
+++ b/plan9/pwd_plan9.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build !go1.5
 // +build !go1.5
 
 package plan9
diff --git a/plan9/race.go b/plan9/race.go
index 42edd93..62377d2 100644
--- a/plan9/race.go
+++ b/plan9/race.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build plan9 && race
 // +build plan9,race
 
 package plan9
diff --git a/plan9/race0.go b/plan9/race0.go
index c89cf8f..f8da308 100644
--- a/plan9/race0.go
+++ b/plan9/race0.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build plan9 && !race
 // +build plan9,!race
 
 package plan9
diff --git a/plan9/str.go b/plan9/str.go
index 4f7f9ad..55fa8d0 100644
--- a/plan9/str.go
+++ b/plan9/str.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build plan9
 // +build plan9
 
 package plan9
diff --git a/plan9/syscall.go b/plan9/syscall.go
index e7363a2..602473c 100644
--- a/plan9/syscall.go
+++ b/plan9/syscall.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build plan9
 // +build plan9
 
 // Package plan9 contains an interface to the low-level operating system
diff --git a/plan9/syscall_test.go b/plan9/syscall_test.go
index 8f829ba..50b4f68 100644
--- a/plan9/syscall_test.go
+++ b/plan9/syscall_test.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build plan9
 // +build plan9
 
 package plan9_test
diff --git a/plan9/zsyscall_plan9_386.go b/plan9/zsyscall_plan9_386.go
index 6819bc2..3f40b9b 100644
--- a/plan9/zsyscall_plan9_386.go
+++ b/plan9/zsyscall_plan9_386.go
@@ -1,6 +1,7 @@
 // go run mksyscall.go -l32 -plan9 -tags plan9,386 syscall_plan9.go
 // Code generated by the command above; see README.md. DO NOT EDIT.
 
+//go:build plan9 && 386
 // +build plan9,386
 
 package plan9
diff --git a/plan9/zsyscall_plan9_amd64.go b/plan9/zsyscall_plan9_amd64.go
index 418abbb..0e6a96a 100644
--- a/plan9/zsyscall_plan9_amd64.go
+++ b/plan9/zsyscall_plan9_amd64.go
@@ -1,6 +1,7 @@
 // go run mksyscall.go -l32 -plan9 -tags plan9,amd64 syscall_plan9.go
 // Code generated by the command above; see README.md. DO NOT EDIT.
 
+//go:build plan9 && amd64
 // +build plan9,amd64
 
 package plan9
diff --git a/plan9/zsyscall_plan9_arm.go b/plan9/zsyscall_plan9_arm.go
index 3e8a1a5..244c501 100644
--- a/plan9/zsyscall_plan9_arm.go
+++ b/plan9/zsyscall_plan9_arm.go
@@ -1,6 +1,7 @@
 // go run mksyscall.go -l32 -plan9 -tags plan9,arm syscall_plan9.go
 // Code generated by the command above; see README.md. DO NOT EDIT.
 
+//go:build plan9 && arm
 // +build plan9,arm
 
 package plan9
diff --git a/unix/linux/mkall.go b/unix/linux/mkall.go
index 3e28120..70a58d3 100644
--- a/unix/linux/mkall.go
+++ b/unix/linux/mkall.go
@@ -10,6 +10,7 @@
 // the appropriate sources are ready, the program is run as:
 //     go run linux/mkall.go <linux_dir> <glibc_dir>
 
+//go:build ignore
 // +build ignore
 
 package main
diff --git a/unix/mkmerge_test.go b/unix/mkmerge_test.go
index 04ee393..a1463b9 100644
--- a/unix/mkmerge_test.go
+++ b/unix/mkmerge_test.go
@@ -105,6 +105,7 @@
 
 // build directives for arch{{.}}
 
+//go:build goos && arch{{.}}
 // +build goos,arch{{.}}
 
 package main
@@ -190,6 +191,7 @@
 
 // build directives for arch{{.}}
 
+//go:build goos && arch{{.}}
 // +build goos,arch{{.}}
 
 package main
diff --git a/windows/registry/export_test.go b/windows/registry/export_test.go
index 8badf6f..d02d93f 100644
--- a/windows/registry/export_test.go
+++ b/windows/registry/export_test.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build windows
 // +build windows
 
 package registry
diff --git a/windows/registry/mksyscall.go b/windows/registry/mksyscall.go
index 50c32a3..ee74927 100644
--- a/windows/registry/mksyscall.go
+++ b/windows/registry/mksyscall.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build generate
 // +build generate
 
 package registry
diff --git a/windows/registry/registry_test.go b/windows/registry/registry_test.go
index c934122..e2dd66f 100644
--- a/windows/registry/registry_test.go
+++ b/windows/registry/registry_test.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build windows
 // +build windows
 
 package registry_test
diff --git a/windows/registry/syscall.go b/windows/registry/syscall.go
index e66643c..4173351 100644
--- a/windows/registry/syscall.go
+++ b/windows/registry/syscall.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build windows
 // +build windows
 
 package registry
diff --git a/windows/registry/value.go b/windows/registry/value.go
index f25e7e9..2789f6f 100644
--- a/windows/registry/value.go
+++ b/windows/registry/value.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build windows
 // +build windows
 
 package registry
diff --git a/windows/svc/debug/log.go b/windows/svc/debug/log.go
index e51ab42..6ee64ca 100644
--- a/windows/svc/debug/log.go
+++ b/windows/svc/debug/log.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build windows
 // +build windows
 
 package debug
diff --git a/windows/svc/debug/service.go b/windows/svc/debug/service.go
index e621b87..3b41899 100644
--- a/windows/svc/debug/service.go
+++ b/windows/svc/debug/service.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build windows
 // +build windows
 
 // Package debug provides facilities to execute svc.Handler on console.
diff --git a/windows/svc/eventlog/install.go b/windows/svc/eventlog/install.go
index c76a376..43e324f 100644
--- a/windows/svc/eventlog/install.go
+++ b/windows/svc/eventlog/install.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build windows
 // +build windows
 
 package eventlog
diff --git a/windows/svc/eventlog/log.go b/windows/svc/eventlog/log.go
index 46e5153..a1796fb 100644
--- a/windows/svc/eventlog/log.go
+++ b/windows/svc/eventlog/log.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build windows
 // +build windows
 
 // Package eventlog implements access to Windows event log.
diff --git a/windows/svc/eventlog/log_test.go b/windows/svc/eventlog/log_test.go
index 6fbbd4a..a667b8f 100644
--- a/windows/svc/eventlog/log_test.go
+++ b/windows/svc/eventlog/log_test.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build windows
 // +build windows
 
 package eventlog_test
diff --git a/windows/svc/example/beep.go b/windows/svc/example/beep.go
index dcf2340..b454f59 100644
--- a/windows/svc/example/beep.go
+++ b/windows/svc/example/beep.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build windows
 // +build windows
 
 package main
diff --git a/windows/svc/example/install.go b/windows/svc/example/install.go
index 39cb00d..4e9ac88 100644
--- a/windows/svc/example/install.go
+++ b/windows/svc/example/install.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build windows
 // +build windows
 
 package main
diff --git a/windows/svc/example/main.go b/windows/svc/example/main.go
index 9bf9bbd..a47650f 100644
--- a/windows/svc/example/main.go
+++ b/windows/svc/example/main.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build windows
 // +build windows
 
 // Example service program that beeps.
diff --git a/windows/svc/example/manage.go b/windows/svc/example/manage.go
index 782dbd9..8ba3952 100644
--- a/windows/svc/example/manage.go
+++ b/windows/svc/example/manage.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build windows
 // +build windows
 
 package main
diff --git a/windows/svc/example/service.go b/windows/svc/example/service.go
index 45e4c90..c989abf 100644
--- a/windows/svc/example/service.go
+++ b/windows/svc/example/service.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build windows
 // +build windows
 
 package main
diff --git a/windows/svc/mgr/config.go b/windows/svc/mgr/config.go
index da4df63..0455486 100644
--- a/windows/svc/mgr/config.go
+++ b/windows/svc/mgr/config.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build windows
 // +build windows
 
 package mgr
diff --git a/windows/svc/mgr/mgr.go b/windows/svc/mgr/mgr.go
index 8e78daf..de75f4a 100644
--- a/windows/svc/mgr/mgr.go
+++ b/windows/svc/mgr/mgr.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build windows
 // +build windows
 
 // Package mgr can be used to manage Windows service programs.
diff --git a/windows/svc/mgr/mgr_test.go b/windows/svc/mgr/mgr_test.go
index 7035db2..330cca4 100644
--- a/windows/svc/mgr/mgr_test.go
+++ b/windows/svc/mgr/mgr_test.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build windows
 // +build windows
 
 package mgr_test
diff --git a/windows/svc/mgr/recovery.go b/windows/svc/mgr/recovery.go
index e465cbb..2e042dd 100644
--- a/windows/svc/mgr/recovery.go
+++ b/windows/svc/mgr/recovery.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build windows
 // +build windows
 
 package mgr
diff --git a/windows/svc/mgr/service.go b/windows/svc/mgr/service.go
index 7d735ca..0623fc0 100644
--- a/windows/svc/mgr/service.go
+++ b/windows/svc/mgr/service.go
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build windows
 // +build windows
 
 package mgr