diff --git a/zathura/bookmarks.c b/zathura/bookmarks.c
index 62932db..c16782a 100644
--- a/zathura/bookmarks.c
+++ b/zathura/bookmarks.c
@@ -134,7 +134,7 @@ zathura_bookmarks_load(zathura_t* zathura, const gchar* file)
 }
 
 int
-zathura_bookmarks_compare(zathura_bookmark_t* lhs, zathura_bookmark_t* rhs)
+zathura_bookmarks_compare(const zathura_bookmark_t* lhs, const zathura_bookmark_t* rhs)
 {
   if (lhs == NULL && rhs == NULL) {
     return 0;
diff --git a/zathura/bookmarks.h b/zathura/bookmarks.h
index 980cca0..5119c90 100644
--- a/zathura/bookmarks.h
+++ b/zathura/bookmarks.h
@@ -61,6 +61,6 @@ bool zathura_bookmarks_load(zathura_t* zathura, const gchar* file);
  * @param rhs a bookmark
  * @returns g_strcmp0(lhs->id, rhs->id)
  */
-int zathura_bookmarks_compare(zathura_bookmark_t* lhs, zathura_bookmark_t* rhs);
+int zathura_bookmarks_compare(const zathura_bookmark_t* lhs, const zathura_bookmark_t* rhs);
 
 #endif // BOOKMARKS_H