diff --git a/b2/util.c b/b2/util.c
index 8b40791..15701bd 100644
--- a/b2/util.c
+++ b/b2/util.c
@@ -38,3 +38,21 @@ const char *unique(const char *s)
 	}
 	return u;
 }
+
+
+const char *unique_n(const char *s, int n)
+{
+	char *tmp, *u;
+
+	if (!tree)
+		tree = g_tree_new(comp);
+	tmp = stralloc_n(s, n);
+	u = g_tree_lookup(tree, tmp);
+	if (u) {
+		free(tmp);
+		return u;
+	} else {
+		g_tree_insert(tree, tmp, tmp);
+		return tmp;
+	}
+}
diff --git a/b2/util.h b/b2/util.h
index b8084d6..4ec841a 100644
--- a/b2/util.h
+++ b/b2/util.h
@@ -50,5 +50,6 @@ static inline char *stralloc_n(const char *s, int n)
 
 
 const char *unique(const char *s);
+const char *unique_n(const char *s, int n);
 
 #endif /* !UTIL_H */