diff --git a/kvlist.c b/kvlist.c
index 4f56a38..e0a8acb 100644
--- a/kvlist.c
+++ b/kvlist.c
@@ -24,17 +24,17 @@
 
 #include "kvlist.h"
 
-int kvlist_strlen(struct kvlist *kv, void *data)
+int kvlist_strlen(struct kvlist *kv, const void *data)
 {
 	return strlen(data) + 1;
 }
 
-int kvlist_blob_len(struct kvlist *kv, void *data)
+int kvlist_blob_len(struct kvlist *kv, const void *data)
 {
 	return blob_pad_len(data);
 }
 
-void kvlist_init(struct kvlist *kv, int (*get_len)(struct kvlist *kv, void *data))
+void kvlist_init(struct kvlist *kv, int (*get_len)(struct kvlist *kv, const void *data))
 {
 	avl_init(&kv->avl, avl_strcmp, false, NULL);
 	kv->get_len = get_len;
@@ -71,7 +71,7 @@ bool kvlist_delete(struct kvlist *kv, const char *name)
 	return !!node;
 }
 
-void kvlist_set(struct kvlist *kv, const char *name, void *data)
+void kvlist_set(struct kvlist *kv, const char *name, const void *data)
 {
 	struct kvlist_node *node;
 	char *name_buf;
diff --git a/kvlist.h b/kvlist.h
index a4e1b1d..0d35b46 100644
--- a/kvlist.h
+++ b/kvlist.h
@@ -23,7 +23,7 @@
 struct kvlist {
 	struct avl_tree avl;
 
-	int (*get_len)(struct kvlist *kv, void *data);
+	int (*get_len)(struct kvlist *kv, const void *data);
 };
 
 struct kvlist_node {
@@ -42,13 +42,13 @@ struct kvlist_node {
 	     value = (void *) (__avl_list_to_kv(__ptr_to_kv(value)->avl.list.next))->data,	\
 	     name = (const char *) __ptr_to_kv(value)->avl.key)
 
-void kvlist_init(struct kvlist *kv, int (*get_len)(struct kvlist *kv, void *data));
+void kvlist_init(struct kvlist *kv, int (*get_len)(struct kvlist *kv, const void *data));
 void kvlist_free(struct kvlist *kv);
 void *kvlist_get(struct kvlist *kv, const char *name);
-void kvlist_set(struct kvlist *kv, const char *name, void *data);
+void kvlist_set(struct kvlist *kv, const char *name, const void *data);
 bool kvlist_delete(struct kvlist *kv, const char *name);
 
-int kvlist_strlen(struct kvlist *kv, void *data);
-int kvlist_blob_len(struct kvlist *kv, void *data);
+int kvlist_strlen(struct kvlist *kv, const void *data);
+int kvlist_blob_len(struct kvlist *kv, const void *data);
 
 #endif