diff --git a/src/os/wait_unimp.go b/src/os/wait_unimp.go
index 9bb85da80262b..c1f66ca1554d0 100644
--- a/src/os/wait_unimp.go
+++ b/src/os/wait_unimp.go
@@ -2,8 +2,12 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build aix || darwin || (js && wasm) || openbsd || solaris
-// +build aix darwin js,wasm openbsd solaris
+// aix, darwin, js/wasm, openbsd and solaris don't implement
+// waitid/wait6. netbsd implements wait6, but that is causing test
+// failures, see issue #48789.
+
+//go:build aix || darwin || (js && wasm) || netbsd || openbsd || solaris
+// +build aix darwin js,wasm netbsd openbsd solaris
 
 package os
 
@@ -11,7 +15,9 @@ package os
 // succeed immediately, and reports whether it has done so.
 // It does not actually call p.Wait.
 // This version is used on systems that do not implement waitid,
-// or where we have not implemented it yet.
+// or where we have not implemented it yet. Note that this is racy:
+// a call to Process.Signal can in an extremely unlikely case send a
+// signal to the wrong process, see issue #13987.
 func (p *Process) blockUntilWaitable() (bool, error) {
 	return false, nil
 }
diff --git a/src/os/wait_wait6.go b/src/os/wait_wait6.go
index 45b370a802e8a..51193401f9383 100644
--- a/src/os/wait_wait6.go
+++ b/src/os/wait_wait6.go
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build dragonfly || freebsd || netbsd
-// +build dragonfly freebsd netbsd
+//go:build dragonfly || freebsd
+// +build dragonfly freebsd
 
 package os