diff --git a/include/eval0eval.h b/include/eval0eval.h
index f950512adfd..c869924a81f 100644
--- a/include/eval0eval.h
+++ b/include/eval0eval.h
@@ -62,7 +62,7 @@ void
 eval_node_copy_and_alloc_val(
 /*=========================*/
 	que_node_t*	node,	/* in: query graph node */
-	byte*		str,	/* in: binary string */
+	const byte*	str,	/* in: binary string */
 	ulint		len);	/* in: string length or UNIV_SQL_NULL */
 /*********************************************************************
 Copies a query node value to another node. */
diff --git a/include/eval0eval.ic b/include/eval0eval.ic
index caffa2e0bfd..5e322eebc60 100644
--- a/include/eval0eval.ic
+++ b/include/eval0eval.ic
@@ -200,7 +200,7 @@ void
 eval_node_copy_and_alloc_val(
 /*=========================*/
 	que_node_t*	node,	/* in: query graph node */
-	byte*		str,	/* in: binary string */
+	const byte*	str,	/* in: binary string */
 	ulint		len)	/* in: string length or UNIV_SQL_NULL */
 {
 	byte*		data;