diff --git a/gcc/config/nvptx/nvptx.opt b/gcc/config/nvptx/nvptx.opt
index 58eddeeabf42ebf413f5bee20c2558f8109b7775..55a10572dd19066160c2ba23024d8299077f8305 100644
--- a/gcc/config/nvptx/nvptx.opt
+++ b/gcc/config/nvptx/nvptx.opt
@@ -25,7 +25,8 @@
 
 m64
 Target RejectNegative Mask(ABI64)
-Generate code for a 64-bit ABI.
+Ignored, but preserved for backward compatibility.  Only 64-bit ABI is
+supported.
 
 mmainkernel
 Target RejectNegative