diff --git a/ll-merge.h b/ll-merge.h
--- /dev/null
+++ b/ll-merge.h
@@ -0,0 +1,15 @@
+/*
+ * Low level 3-way in-core file merge.
+ */
+
+#ifndef LL_MERGE_H
+#define LL_MERGE_H
+
+int ll_merge(mmbuffer_t *result_buf,
+ const char *path,
+ mmfile_t *ancestor,
+ mmfile_t *ours, const char *our_label,
+ mmfile_t *theirs, const char *their_label,
+ int virtual_ancestor);
+
+#endif