diff --git a/.gitignore b/.gitignore
index 04e66d7..183f3ce 100644
--- a/.gitignore
+++ b/.gitignore
@@ -33,6 +33,8 @@
 
 /.idea/
 /cmake-*/
+/build/
 /build-*/
-/test/catch.hpp
+/_codeql_build_dir/
+_codeql_detected_source_root
 
diff --git a/deps/fbitset b/deps/fbitset
index 1f1a3db..c3ca474 160000
--- a/deps/fbitset
+++ b/deps/fbitset
@@ -1 +1 @@
-Subproject commit 1f1a3db3dd86dacbdfc422bed91a1d79f87230e7
+Subproject commit c3ca47404ac195a96f87ccf94ea66b3fc593cff5
diff --git a/include/libparenth.hpp b/include/libparenth.hpp
index f86b814..7e6e5e8 100644
--- a/include/libparenth.hpp
+++ b/include/libparenth.hpp
@@ -329,13 +329,14 @@ class Parenther {
             auto bsums = std::move(q_.top());
             q_.pop();
 
+            auto has_top_idx = bsums.curr_sums.count() > 0;
             auto top_idx = bsums.curr_sums.find_last();
             auto next_idx = top_idx + 1;
             if (next_idx < sums_.size()) {
 
                 // Augmentation.
                 bsums.lsc = bsums.lsc * parenther_.dims_[sums_[next_idx]];
-                if (top_idx < 0) {
+                if (!has_top_idx) {
                     bsums.lsc = bsums.lsc * Dim(2l);
                 }
                 bsums.curr_sums.set(next_idx);
@@ -345,7 +346,7 @@ class Parenther {
                 }
 
                 // Shift.
-                if (top_idx >= 0) {
+                if (has_top_idx) {
                     const auto& top_dim = parenther_.dims_[sums_[top_idx]];
                     assert(bsums.lsc % top_dim == 0);
                     bsums.lsc = bsums.lsc / top_dim;
diff --git a/test/matrixchain.cpp b/test/matrixchain.cpp
index 642517b..6d41231 100644
--- a/test/matrixchain.cpp
+++ b/test/matrixchain.cpp
@@ -17,8 +17,8 @@
 
 // Disable Catch2's range detection for fbitset by providing stream insertion operator
 namespace fbitset {
-    template<int N>
-    inline std::ostream& operator<<(std::ostream& os, const Fbitset<N>& fs) {
+    template<Size N, typename L, typename E>
+    inline std::ostream& operator<<(std::ostream& os, const Fbitset<N, L, E>& fs) {
         os << "Fbitset<" << N << ">{count=" << fs.count() << "}";
         return os;
     }