diff --git a/src/util/hashtable.h b/src/util/hashtable.h
index 70f0d7085..6ca04b0d7 100644
--- a/src/util/hashtable.h
+++ b/src/util/hashtable.h
@@ -636,6 +636,13 @@ public:
         return *this;
     }
 
+    core_hashtable& operator=(core_hashtable && other) {
+        if (this == &other) return *this;
+        delete_table();
+        std::swap(*this, other);
+        return *this;
+    }
+
 #ifdef Z3DEBUG
     bool check_invariant() {
         // The capacity must always be a power of two.
diff --git a/src/util/s_integer.h b/src/util/s_integer.h
index 7d17f6f22..5accf7b4b 100644
--- a/src/util/s_integer.h
+++ b/src/util/s_integer.h
@@ -34,10 +34,6 @@ public:
     struct hash_proc {  unsigned operator()(s_integer const& r) const { return r.hash(); }  };
     struct eq_proc { bool operator()(s_integer const& r1, s_integer const& r2) const { return r1 == r2; } };
 
-    void swap(s_integer & n) noexcept {
-        std::swap(m_val, n.m_val);
-    }
-
     std::string to_string() const;
 
 public: