diff --git a/src/opt/eslim/eslimCirMan.cpp b/src/opt/eslim/eslimCirMan.cpp
index 5b0fa6a785..dd9fa1068d 100644
--- a/src/opt/eslim/eslimCirMan.cpp
+++ b/src/opt/eslim/eslimCirMan.cpp
@@ -967,7 +967,8 @@ namespace eSLIM {
     for (int i = 1; i <= getNofPos(); i++) {
       insertSorted(nodes[nodes.size() - i].get(), nodes_aux, replacement, out_map, invec);
     }
-    assert (nodes_aux.size() <= nodes.size());
+    // Account for replacement growth; primary outputs are not yet in nodes_aux.
+    assert (nodes_aux.size() <= nodes.size() - size_diff - getNofPos());
     int current_depth = 0;
     for (int i = 0; i < getNofPos(); i++) {
       int po_id = getNofObjs() - getNofPos() + i;
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 7fb1208539..db3263cbf1 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -1,5 +1,10 @@
 add_subdirectory(gia)
 
+add_executable(eslim_replace eslim_replace.cpp)
+target_link_libraries(eslim_replace PRIVATE libabc)
+add_test(NAME eslim_replace COMMAND eslim_replace)
+set_tests_properties(eslim_replace PROPERTIES SKIP_RETURN_CODE 77)
+
 # The eSLIM2 oracles are local, uncommitted test assets. A fresh checkout must
 # still configure and build when those files are absent.
 set(ESLIM2_LOCAL_TEST_NAMES small_exact small_timing small_order area_refinement windows instances)
diff --git a/test/eslim_replace.cpp b/test/eslim_replace.cpp
new file mode 100644
index 0000000000..4704196ff3
--- /dev/null
+++ b/test/eslim_replace.cpp
@@ -0,0 +1,112 @@
+// Regression for replacing an eSLIM window with a larger equivalent circuit.
+// Build both libabc and the test with assertions enabled; NDEBUG builds skip it.
+// Run from the repository root:
+// cmake -S . -B build -DCMAKE_BUILD_TYPE=Debug
+// cmake --build build --config Debug --target eslim_replace
+// ctest --test-dir build -C Debug -R '^eslim_replace$' --output-on-failure
+#include <cstdio>
+
+#ifdef NDEBUG
+int main() {
+    std::puts("SKIP: eslim_replace requires assertions in libabc and the test; use a Debug build.");
+    return 77;
+}
+#else
+
+#include <algorithm>
+#include <cassert>
+#include <set>
+#include <vector>
+
+#include "opt/eslim/eslimCirMan.hpp"
+#include "opt/eslim/subcircuit.hpp"
+
+ABC_NAMESPACE_USING_NAMESPACE
+
+// Every gate is reachable, and the output is a & b for any positive size.
+static eSLIM::eSLIMCirMan makeCircuit(int gates) {
+    eSLIM::eSLIMCirMan circuit(gates + 4);
+    int a = circuit.addPi();
+    int b = circuit.addPi();
+    int output = circuit.addNode({a, b}, 8);
+    for (int i = 1; i < gates; ++i)
+        output = circuit.addNode({output, i % 2 ? a : b}, 8);
+    circuit.addPo(output, false);
+    return circuit;
+}
+
+static void checkCircuit(const eSLIM::eSLIMCirMan& circuit, int gates) {
+    assert(circuit.getNofPis() == 2);
+    assert(circuit.getNofPos() == 1);
+    assert(circuit.getNofGates() == gates);
+    assert(circuit.getNofObjs() == gates + 4);
+    assert(circuit.getDepth() == gates + 1);
+
+    std::set<const eSLIM::eSLIMCirObj*> objects;
+    std::set<unsigned int> ids;
+    for (int i = 0; i < circuit.getNofObjs(); ++i)
+        objects.insert(&circuit.getObj(i));
+    for (int i = 0; i < circuit.getNofObjs(); ++i) {
+        const auto& node = circuit.getObj(i);
+        assert(node.node_id == i);
+        if (i > 0) {
+            bool inserted = ids.insert(node.getId()).second;
+            assert(inserted);
+        }
+        int depth = 0;
+        for (auto fanin : node.fanins) {
+            assert(objects.count(fanin) == 1);
+            assert(fanin->node_id >= 0 && fanin->node_id < i);
+            assert(fanin->fanouts.count(const_cast<eSLIM::eSLIMCirObj*>(&node)) == 1);
+            depth = std::max(depth, fanin->depth + 1);
+        }
+        assert(node.depth == depth);
+        for (auto fanout : node.fanouts) {
+            assert(objects.count(fanout) == 1);
+            assert(std::find(fanout->fanins.begin(), fanout->fanins.end(), &node) != fanout->fanins.end());
+        }
+        if (circuit.isGate(i))
+            assert(!node.fanouts.empty());
+    }
+
+    // Exhaustively check equivalence to a & b, including the PO truth table.
+    for (unsigned input = 0; input < 4; ++input) {
+        std::vector<unsigned> values(circuit.getNofObjs(), 0);
+        values[1] = input & 1;
+        values[2] = (input >> 1) & 1;
+        for (int i = 3; i < circuit.getNofObjs(); ++i) {
+            const auto& node = circuit.getObj(i);
+            unsigned row = 0;
+            for (unsigned j = 0; j < node.fanins.size(); ++j)
+                row |= values[node.fanins[j]->node_id] << j;
+            values[i] = (node.tt >> row) & 1;
+        }
+        assert(values.back() == (input == 3));
+    }
+}
+
+int main() {
+    auto circuit = makeCircuit(1);
+    checkCircuit(circuit, 1);
+    // The first replacement grows by two gates: before appending the PO,
+    // nodes_aux contains six objects, while the original has only five.
+    // Also exercise equal size, growth by one, and shrinking on the same manager.
+    for (int gates : {3, 3, 4, 1}) {
+        {
+            auto replacement = makeCircuit(gates);
+            checkCircuit(replacement, gates);
+            std::vector<int> nodes;
+            for (int i = 3; i < circuit.getNofObjs() - 1; ++i)
+                nodes.push_back(i);
+            circuit.incrementTraversalId();
+            auto subcir = eSLIM::Subcircuit::getSubcircuitBare(circuit, nodes.begin(), nodes.end());
+            assert((subcir.inputs == std::vector<int>{1, 2}));
+            assert(subcir.outputs.size() == 1);
+            circuit.replace(replacement, subcir);
+        }
+        // Check ownership and links after the replacement manager is destroyed.
+        checkCircuit(circuit, gates);
+    }
+    std::puts("PASS: eSLIM replacement counts, graph consistency and exhaustive equivalence");
+}
+#endif