diff --git a/src/cmd/compile/internal/base/flag.go b/src/cmd/compile/internal/base/flag.go
index 0056f83059e..49e004cf185 100644
--- a/src/cmd/compile/internal/base/flag.go
+++ b/src/cmd/compile/internal/base/flag.go
@@ -58,7 +58,7 @@ type CmdFlags struct {
 	E CountFlag    "help:\"debug symbol export\""
 	I func(string) "help:\"add `directory` to import search path\""
 	K CountFlag    "help:\"debug missing line numbers\""
-	L CountFlag    "help:\"show full file names in error messages\""
+	L CountFlag    "help:\"also show actual source file names in error messages for positions affected by //line directives\""
 	N CountFlag    "help:\"disable optimizations\""
 	S CountFlag    "help:\"print assembly listing\""
 	// V is added by objabi.AddVersionFlag