diff --git a/src/pkg/os/exec.go b/src/pkg/os/exec.go
index a7430ef7f7..9ae81c0d5a 100644
--- a/src/pkg/os/exec.go
+++ b/src/pkg/os/exec.go
@@ -70,9 +70,13 @@ const (
 	WNOHANG = syscall.WNOHANG;	// Don't wait if no process has exited.
 	WSTOPPED = syscall.WSTOPPED;	// If set, status of stopped subprocesses is also reported.
 	WUNTRACED = WSTOPPED;
-	WRUSAGE = 1<<30;	// Record resource usage.
+	WRUSAGE = 1<<20;	// Record resource usage.
 )
 
+// WRUSAGE must not be too high a bit, to avoid clashing with Linux's
+// WCLONE, WALL, and WNOTHREAD flags, which sit in the top few bits of
+// the options
+
 // Wait waits for process pid to exit or stop, and then returns a
 // Waitmsg describing its status and an Error, if any. The options
 // (WNOHANG etc.) affect the behavior of the Wait call.