diff --git a/pyci/src/common.cpp b/pyci/src/common.cpp
index b6657be..675b58a 100644
--- a/pyci/src/common.cpp
+++ b/pyci/src/common.cpp
@@ -30,7 +30,7 @@ long get_num_threads(void) {
 }
 
 long end_chunk_idx(const long thread_idx, const long num_threads, const long sideLength) {
-    return ceil(sqrt(thread_idx / num_threads) * sideLength);
+    return ceil(static_cast<double>(thread_idx) / static_cast<double>(num_threads) * sideLength);
 }
 
 void set_num_threads(const long n) {
diff --git a/pyci/src/hci.cpp b/pyci/src/hci.cpp
index e934c84..10ff9d7 100644
--- a/pyci/src/hci.cpp
+++ b/pyci/src/hci.cpp
@@ -267,11 +267,9 @@ long add_hci(const SQuantOp &ham, WfnType &wfn, const double *coeffs, const doub
         v_threads.emplace_back(&hci_thread<WfnType>, std::ref(ham), std::ref(wfn),
                                std::ref(v_wfns.back()), coeffs, eps, start, end);
     }
-    long n = 0;
-    for (auto &thread : v_threads) {
-        thread.join();
-        wfn.add_dets_from_wfn(v_wfns[n++]);
-    }
+    for (auto &thread : v_threads) thread.join();
+    for (auto &wf : v_wfns) wfn.add_dets_from_wfn(wf);
+
     return wfn.ndet - ndet_old;
 }