diff --git a/src/sysdep.h b/src/sysdep.h
index 6568980a..53b45119 100644
--- a/src/sysdep.h
+++ b/src/sysdep.h
@@ -178,11 +178,11 @@ void *memcpy ();
 #endif /* sun */
 #endif /* STDC_HEADERS */
 
-/* Some systems don't provide MAP_FAILED, a symbolic constant for the
-   value returned by mmap() when it doesn't work.  Usually, this
-   constant should be -1.  This only makes sense for files that use
-   mmap() and include sys/mman.h *before* sysdep.h, but doesn't hurt
-   others.  */
+/* Some systems (Linux libc5, "NCR MP-RAS 3.0", and others) don't
+   provide MAP_FAILED, a symbolic constant for the value returned by
+   mmap() when it doesn't work.  Usually, this constant should be -1.
+   This only makes sense for files that use mmap() and include
+   sys/mman.h *before* sysdep.h, but doesn't hurt others.  */
 
 #ifndef MAP_FAILED
 # define MAP_FAILED ((void *) -1)