diff --git a/src/os/exec_plan9.go b/src/os/exec_plan9.go
index 676be36ac7..6b4d28c93d 100644
--- a/src/os/exec_plan9.go
+++ b/src/os/exec_plan9.go
@@ -11,9 +11,10 @@ import (
 	"time"
 )
 
-// The only signal values guaranteed to be present on all systems
-// are Interrupt (send the process an interrupt) and Kill (force
-// the process to exit).
+// The only signal values guaranteed to be present in the os package
+// on all systems are Interrupt (send the process an interrupt) and
+// Kill (force the process to exit). Interrupt is not implemented on
+// Windows; using it with os.Process.Signal will return an error.
 var (
 	Interrupt Signal = syscall.Note("interrupt")
 	Kill      Signal = syscall.Note("kill")
diff --git a/src/os/exec_posix.go b/src/os/exec_posix.go
index 3cf38b68ad..fb220c8a5a 100644
--- a/src/os/exec_posix.go
+++ b/src/os/exec_posix.go
@@ -10,9 +10,10 @@ import (
 	"syscall"
 )
 
-// The only signal values guaranteed to be present on all systems
-// are Interrupt (send the process an interrupt) and Kill (force
-// the process to exit).
+// The only signal values guaranteed to be present in the os package
+// on all systems are Interrupt (send the process an interrupt) and
+// Kill (force the process to exit). Interrupt is not implemented on
+// Windows; using it with os.Process.Signal will return an error.
 var (
 	Interrupt Signal = syscall.SIGINT
 	Kill      Signal = syscall.SIGKILL