diff --git a/src/message.c b/src/message.c
index 02380e9..becb280 100644
--- a/src/message.c
+++ b/src/message.c
@@ -1820,8 +1820,8 @@
 	    *sp = str + 1;
     }
     else
-	// single-byte character or illegal byte
-	*sp = str + 1;
+	// single-byte character, NUL or illegal byte
+	*sp = str + (*str == NUL ? 0 : 1);
 
     // Make special keys and C0 control characters in <> form, also <M-Space>.
     // Use <Space> only for lhs of a mapping.