diff --git a/rbtree.c b/rbtree.c
index 7e13bffb0..618b4f8df 100644
--- a/rbtree.c
+++ b/rbtree.c
@@ -12,9 +12,9 @@
 
 #include "rbtree.h"
 
-const struct rbtree *rb_search(const struct rbtree *tree, uint64_t key)
+struct rbtree *rb_search(struct rbtree *tree, uint64_t key)
 {
-    const struct rbtree *best = NULL;
+    struct rbtree *best = NULL;
 
     while (tree) {
 	if (tree->key == key)
diff --git a/rbtree.h b/rbtree.h
index d24daf350..e6d5c824d 100644
--- a/rbtree.h
+++ b/rbtree.h
@@ -14,6 +14,6 @@ struct rbtree {
 };
 
 struct rbtree *rb_insert(struct rbtree *, struct rbtree *);
-const struct rbtree *rb_search(const struct rbtree *, uint64_t);
+struct rbtree *rb_search(struct rbtree *, uint64_t);
 
 #endif /* NASM_RBTREE_H */