diff --git a/ConflictSet.cpp b/ConflictSet.cpp
index 84313db..742abae 100644
--- a/ConflictSet.cpp
+++ b/ConflictSet.cpp
@@ -374,10 +374,8 @@ inline void Node16::copyChildrenAndKeyFrom(const Node48 &other) {
   other.bitSet.forEachInRange(
       [&](int c) {
         // Suppress a false positive -Waggressive-loop-optimizations warning
-        // in gcc. `assume` doesn't work for some reason.
-        if (!(i < Node16::kMaxNodes)) {
-          __builtin_unreachable(); // GCOVR_EXCL_LINE
-        }
+        // in gcc
+        assume(i < Node16::kMaxNodes);
         index[i] = c;
         children[i] = other.children[other.index[c]];
         assert(children[i].child->parent == &other);
@@ -430,10 +428,8 @@ inline void Node48::copyChildrenAndKeyFrom(const Node256 &other) {
   bitSet.forEachInRange(
       [&](int c) {
         // Suppress a false positive -Waggressive-loop-optimizations warning
-        // in gcc. `assume` doesn't work for some reason.
-        if (!(i < Node48::kMaxNodes)) {
-          __builtin_unreachable(); // GCOVR_EXCL_LINE
-        }
+        // in gcc.
+        assume(i < Node48::kMaxNodes);
         index[c] = i;
         children[i] = other.children[c];
         assert(children[i].child->parent == &other);