diff --git a/src/problems/unconstrain.cpp b/src/problems/unconstrain.cpp
index 916d81dd8..fc3a6da56 100644
--- a/src/problems/unconstrain.cpp
+++ b/src/problems/unconstrain.cpp
@@ -248,13 +248,14 @@ vector_double unconstrain::batch_fitness(const vector_double &xs) const
     vector_double original_fitness(m_problem.batch_fitness(xs));
     const vector_double::size_type nx = m_problem.get_nx();
     const vector_double::size_type n_dvs = xs.size() / nx;
-    vector_double::size_type nobj = m_problem.get_nobj();
+    const vector_double::size_type nobj = m_problem.get_nobj();
+    const vector_double::size_type nf = m_problem.get_nf();
     vector_double retval;
     retval.resize(safe<vector_double::size_type>(n_dvs) * nobj);
-    vector_double y(nobj);
+    vector_double y(nf);
     vector_double z; // will be resized in penalize if necessary.
     for (vector_double::size_type i = 0; i < n_dvs; ++i) {
-        std::copy(original_fitness.data() + i * nobj, original_fitness.data() + (i + 1) * nobj, y.data());
+        std::copy(original_fitness.data() + i * nf, original_fitness.data() + (i + 1) * nf, y.data());
         penalize(y, z);
         std::copy(z.data(), z.data() + nobj, retval.data() + i * nobj);
     }
diff --git a/tests/unconstrain.cpp b/tests/unconstrain.cpp
index cbef04867..f0fa00d83 100644
--- a/tests/unconstrain.cpp
+++ b/tests/unconstrain.cpp
@@ -332,4 +332,11 @@ BOOST_AUTO_TEST_CASE(unconstrain_batch_test)
     bfe default_bfe{};
     population pop{p0, default_bfe, 20u};
     BOOST_CHECK(bf0::s_counter == 1u);
+
+    // through batch_fitness
+    vector_double::size_type bs = 10;
+    vector_double xs(p0.get_nx() * bs, 1.);
+    vector_double ys = t.batch_fitness(xs);
+    BOOST_CHECK(ys.size() == t.get_nobj() * bs);
+    BOOST_CHECK(bf0::s_counter == 2u);
 }