diff --git a/lib/libalpm/alpm_list.c b/lib/libalpm/alpm_list.c
index 80aa558d..80ba1ee7 100644
--- a/lib/libalpm/alpm_list.c
+++ b/lib/libalpm/alpm_list.c
@@ -657,12 +657,12 @@ char SYMEXPORT *alpm_list_find_str(const alpm_list_t *haystack,
  * @param onlyright pointer to the second result list
  *
  */
-void SYMEXPORT alpm_list_diff_sorted(alpm_list_t *left,
-		alpm_list_t *right, alpm_list_fn_cmp fn,
+void SYMEXPORT alpm_list_diff_sorted(const alpm_list_t *left,
+		const alpm_list_t *right, alpm_list_fn_cmp fn,
 		alpm_list_t **onlyleft, alpm_list_t **onlyright)
 {
-	alpm_list_t *l = left;
-	alpm_list_t *r = right;
+	const alpm_list_t *l = left;
+	const alpm_list_t *r = right;
 
 	if(!onlyleft && !onlyright) {
 		return;
diff --git a/lib/libalpm/alpm_list.h b/lib/libalpm/alpm_list.h
index fcab3014..bd639f7d 100644
--- a/lib/libalpm/alpm_list.h
+++ b/lib/libalpm/alpm_list.h
@@ -78,7 +78,7 @@ void *alpm_list_find(const alpm_list_t *haystack, const void *needle, alpm_list_
 void *alpm_list_find_ptr(const alpm_list_t *haystack, const void *needle);
 char *alpm_list_find_str(const alpm_list_t *haystack, const char *needle);
 alpm_list_t *alpm_list_diff(const alpm_list_t *lhs, const alpm_list_t *rhs, alpm_list_fn_cmp fn);
-void alpm_list_diff_sorted(alpm_list_t *left, alpm_list_t *right,
+void alpm_list_diff_sorted(const alpm_list_t *left, const alpm_list_t *right,
 		alpm_list_fn_cmp fn, alpm_list_t **onlyleft, alpm_list_t **onlyright);
 
 #ifdef __cplusplus