diff --git a/src/modules/math/wrap_Math.cpp b/src/modules/math/wrap_Math.cpp
index 1e91e3675..e1de15c38 100644
--- a/src/modules/math/wrap_Math.cpp
+++ b/src/modules/math/wrap_Math.cpp
@@ -179,7 +179,7 @@ int w_triangulate(lua_State *L)
 	}
 
 	if (vertices.size() < 3)
-		return luaL_error(L, "Need at least 3 vertices to triangulate");
+		return luaL_error(L, "Need at least 3 vertices to triangulate (got %d).", (int)vertices.size());
 
 	std::vector<Triangle> triangles;