diff --git a/src/test/heap.cpp b/src/test/heap.cpp
index 6a5bc7b9ffe..25a509dc8cd 100644
--- a/src/test/heap.cpp
+++ b/src/test/heap.cpp
@@ -27,7 +27,7 @@ struct lt_proc { bool operator()(int v1, int v2) const { return v1 < v2; } };
 //struct int_hash_proc { unsigned operator()(int v) const { std::cout << "hash " << v << "\n"; VERIFY(v >= 0); return v; }};  
 //typedef int_hashtable<int_hash_proc, default_eq<int> > int_set; 
 typedef heap<lt_proc> int_heap;
-#define N 10000
+#define N 100
 
 static random_gen heap_rand(1);
 
@@ -146,4 +146,3 @@ void tst_heap() {
         tst2();
     }
 }
-
diff --git a/src/util/heap.h b/src/util/heap.h
index c080c6ebde9..71cafeeb895 100644
--- a/src/util/heap.h
+++ b/src/util/heap.h
@@ -55,6 +55,19 @@ class heap : private LT {
     }
 
     bool check_invariant_core(int idx) const {
+        
+        // Check that m_values starts with a dummy value at index 0.
+        if (m_values.empty() || m_values[0] != -1) {
+            return false;
+        }
+
+        // // All indices in m_value2indices that are not used in m_values should be 0
+        // for (int val = 0; val < static_cast<int>(m_value2indices.size()); ++val) {
+        //     if (std::find(m_values.begin(), m_values.end(), val) == m_values.end() && m_value2indices[val] != 0) {
+        //         return false; // Unused indices should have a 0 value
+        //     }
+        // }
+
         if (idx < static_cast<int>(m_values.size())) {
             SASSERT(m_value2indices[m_values[idx]] == idx);
             SASSERT(parent(idx) == 0 || !less_than(m_values[idx], m_values[parent(idx)]));