diff --git a/polar_list_decoder.hh b/polar_list_decoder.hh
index d67dc9d..83ce286 100644
--- a/polar_list_decoder.hh
+++ b/polar_list_decoder.hh
@@ -316,7 +316,7 @@ public:
 		for (int k = 0; k < TYPE::SIZE; ++k)
 			perm[k] = k;
 		std::sort(perm, perm + TYPE::SIZE, [metric](int a, int b) { return metric[a] < metric[b]; });
-		for (int i = 0, r = 0; i < TYPE::SIZE; ++i) {
+		for (int i = 0, r = 0; rank != nullptr && i < TYPE::SIZE; ++i) {
 			if (i > 0 && metric[perm[i-1]] != metric[perm[i]])
 				++r;
 			rank[i] = r;
diff --git a/polar_parity_aided.hh b/polar_parity_aided.hh
index c91eda4..f913d95 100644
--- a/polar_parity_aided.hh
+++ b/polar_parity_aided.hh
@@ -379,7 +379,7 @@ public:
 		for (int k = 0; k < TYPE::SIZE; ++k)
 			perm[k] = k;
 		std::sort(perm, perm + TYPE::SIZE, [metric](int a, int b) { return metric[a] < metric[b]; });
-		for (int i = 0, r = 0; i < TYPE::SIZE; ++i) {
+		for (int i = 0, r = 0; rank != nullptr && i < TYPE::SIZE; ++i) {
 			if (i > 0 && metric[perm[i-1]] != metric[perm[i]])
 				++r;
 			rank[i] = r;