diff --git a/ConflictSet.cpp b/ConflictSet.cpp
index 421dfee..05b9353 100644
--- a/ConflictSet.cpp
+++ b/ConflictSet.cpp
@@ -346,6 +346,7 @@ Node *&getChildExists(Node *self, uint8_t index) {
     return self48->children[self48->index[index]].child;
   } else {
     auto *self256 = static_cast<Node256 *>(self);
+    assert(self256->bitSet.test(index));
     return self256->children[index].child;
   }
   __builtin_unreachable(); // GCOVR_EXCL_LINE
@@ -362,6 +363,7 @@ int64_t getChildMaxVersion(Node *self, uint8_t index) {
     return self48->children[self48->index[index]].childMaxVersion;
   } else {
     auto *self256 = static_cast<Node256 *>(self);
+    assert(self256->bitSet.test(index));
     return self256->children[index].childMaxVersion;
   }
   __builtin_unreachable(); // GCOVR_EXCL_LINE
@@ -1880,6 +1882,7 @@ int64_t &maxVersion(Node *n, ConflictSet::Impl *impl) {
     return n48->children[n48->index[index]].childMaxVersion;
   } else {
     auto *n256 = static_cast<Node256 *>(n);
+    assert(n256->bitSet.test(index));
     return n256->children[index].childMaxVersion;
   }
 }