diff --git a/src/api/dotnet/Context.cs b/src/api/dotnet/Context.cs
index 5bff8960a..cf235b4af 100644
--- a/src/api/dotnet/Context.cs
+++ b/src/api/dotnet/Context.cs
@@ -4940,11 +4940,12 @@ namespace Microsoft.Z3
             // Console.WriteLine("Context Finalizer from " + System.Threading.Thread.CurrentThread.ManagedThreadId);
             Dispose();
 
-            if (refCount == 0)
+            if (refCount == 0 && m_ctx != IntPtr.Zero)
             {
                 m_n_err_handler = null;
-                Native.Z3_del_context(m_ctx);
+                IntPtr ctx = m_ctx;
                 m_ctx = IntPtr.Zero;
+                Native.Z3_del_context(ctx);
             }
             else
                 GC.ReRegisterForFinalize(this);
diff --git a/src/tactic/bv/dt2bv_tactic.cpp b/src/tactic/bv/dt2bv_tactic.cpp
index 6f20fc609..86717c807 100644
--- a/src/tactic/bv/dt2bv_tactic.cpp
+++ b/src/tactic/bv/dt2bv_tactic.cpp
@@ -60,10 +60,15 @@ class dt2bv_tactic : public tactic {
 
         br_status reduce_app(func_decl * f, unsigned num, expr * const * args, expr_ref & result, proof_ref & result_pr) {
             expr_ref a0(m), a1(m);
+            expr_ref_vector _args(m);
             if (m.is_eq(f) && reduce_arg(args[0], a0) && reduce_arg(args[1], a1)) {
                 result = m.mk_eq(a0, a1);
                 return BR_DONE;
             }
+            else if (m.is_distinct(f) && reduce_args(num, args, _args)) {
+                result = m.mk_distinct(_args.size(), _args.c_ptr());
+                return BR_DONE;
+            }
             else if (m_t.m_dt.is_recognizer(f) && reduce_arg(args[0], a0)) {
                 unsigned idx = m_t.m_dt.get_recognizer_constructor_idx(f);
                 a1 = m_t.m_bv.mk_numeral(rational(idx), get_sort(a0));
@@ -75,6 +80,15 @@ class dt2bv_tactic : public tactic {
             }
         }
 
+        bool reduce_args(unsigned sz, expr*const* as, expr_ref_vector& result) {
+            expr_ref tmp(m);
+            for (unsigned i = 0; i < sz; ++i) {
+                if (!reduce_arg(as[i], tmp)) return false;
+                result.push_back(tmp);
+            }
+            return true;
+        }
+
         bool reduce_arg(expr* a, expr_ref& result) {
             expr* b;
             if (m_cache.find(a, b)) {
@@ -203,6 +217,9 @@ class dt2bv_tactic : public tactic {
             if (m.is_eq(a)) {
                 return;
             }
+            if (m.is_distinct(a)) {
+                return;
+            }
             if (m_t.m_dt.is_recognizer(a->get_decl()) &&
                 m_t.is_fd(a->get_arg(0))) {
                 m_t.m_fd_sorts.insert(get_sort(a->get_arg(0)));