diff --git a/sql/handler.cc b/sql/handler.cc
index 40f2af75c2f..d3106efe151 100644
--- a/sql/handler.cc
+++ b/sql/handler.cc
@@ -1107,6 +1107,7 @@ void handler::print_error(int error, myf errflag)
       {
 	/* Key is unknown */
 	str.length(0);
+	str.append("");
 	key_nr= -1;
       }
       else