diff --git a/include/uapi/asm-generic/errno.h b/include/uapi/asm-generic/errno.h
index 1e1ea6e6e7a55b63d9b492b8676e7aaa3f17e1ff..88e0914cf2d99795a889c2e7d9f75ba45732bb30 100644
--- a/include/uapi/asm-generic/errno.h
+++ b/include/uapi/asm-generic/errno.h
@@ -6,7 +6,16 @@
 #define	EDEADLK		35	/* Resource deadlock would occur */
 #define	ENAMETOOLONG	36	/* File name too long */
 #define	ENOLCK		37	/* No record locks available */
-#define	ENOSYS		38	/* Function not implemented */
+
+/*
+ * This error code is special: arch syscall entry code will return
+ * -ENOSYS if users try to call a syscall that doesn't exist.  To keep
+ * failures of syscalls that really do exist distinguishable from
+ * failures due to attempts to use a nonexistent syscall, syscall
+ * implementations should refrain from returning -ENOSYS.
+ */
+#define	ENOSYS		38	/* Invalid system call number */
+
 #define	ENOTEMPTY	39	/* Directory not empty */
 #define	ELOOP		40	/* Too many symbolic links encountered */
 #define	EWOULDBLOCK	EAGAIN	/* Operation would block */