diff --git a/src/util/script_state.cpp b/src/util/script_state.cpp
index c345ab867..31fa91094 100644
--- a/src/util/script_state.cpp
+++ b/src/util/script_state.cpp
@@ -40,8 +40,8 @@ void open_extra(lua_State * L);
 static char g_weak_ptr_key; // key for Lua registry (used at get_weak_ptr and save_weak_ptr)
 
 struct script_state::imp {
-    lua_State *           m_state;
-    recursive_mutex       m_mutex;
+    lua_State * m_state;
+    mutex       m_mutex;
     std::unordered_set<std::string> m_imported_modules;
 
     static std::weak_ptr<imp> * get_weak_ptr(lua_State * L) {
@@ -100,12 +100,12 @@ struct script_state::imp {
     }
 
     void dofile(char const * fname) {
-        lock_guard<recursive_mutex> lock(m_mutex);
+        lock_guard<mutex> lock(m_mutex);
         ::lean::dofile(m_state, fname);
     }
 
     void dostring(char const * str) {
-        lock_guard<recursive_mutex> lock(m_mutex);
+        lock_guard<mutex> lock(m_mutex);
         ::lean::dostring(m_state, str);
     }
 
@@ -162,7 +162,7 @@ bool script_state::import_explicit(char const * str) {
     return m_ptr->import_explicit(str);
 }
 
-recursive_mutex & script_state::get_mutex() {
+mutex & script_state::get_mutex() {
     return m_ptr->m_mutex;
 }
 
@@ -454,8 +454,7 @@ public:
             m_thread.join();
     }
 
-    int wait(lua_State * src) {
-        m_thread.join();
+    int copy_result(lua_State * src) {
         if (m_exception)
             m_exception->rethrow();
         return m_state.apply([&](lua_State * S) {
@@ -468,6 +467,10 @@ public:
             });
     }
 
+    void wait() {
+        m_thread.join();
+    }
+
     void request_interrupt() {
         m_thread.request_interrupt();
     }
@@ -552,7 +555,10 @@ static int thread_interrupt(lua_State * L) {
 }
 
 int thread_wait(lua_State * L) {
-    return to_thread(L, 1).wait(L);
+    auto & t = to_thread(L, 1);
+    script_state st = to_script_state(L);
+    st.exec_unprotected([&]() { t.wait(); });
+    return t.copy_result(L);
 }
 
 static const struct luaL_Reg thread_m[] = {
diff --git a/src/util/script_state.h b/src/util/script_state.h
index ff1a1d2ba..d4a931288 100644
--- a/src/util/script_state.h
+++ b/src/util/script_state.h
@@ -20,7 +20,7 @@ public:
 private:
     std::shared_ptr<imp> m_ptr;
     friend script_state to_script_state(lua_State * L);
-    recursive_mutex & get_mutex();
+    mutex & get_mutex();
     lua_State * get_state();
     friend class data_channel;
 public:
@@ -60,7 +60,7 @@ public:
     */
     template<typename F>
     typename std::result_of<F(lua_State * L)>::type apply(F && f) {
-        lock_guard<recursive_mutex> lock(get_mutex());
+        lock_guard<mutex> lock(get_mutex());
         return f(get_state());
     }
 
@@ -74,13 +74,13 @@ public:
     */
     template<typename F>
     void exec_unprotected(F && f) {
-        unlock_guard<recursive_mutex> unlock(get_mutex());
+        unlock_guard unlock(get_mutex());
         f();
     }
 
     template<typename F>
     void exec_protected(F && f) {
-        lock_guard<recursive_mutex> lock(get_mutex());
+        lock_guard<mutex> lock(get_mutex());
         f();
     }
 };
diff --git a/src/util/unlock_guard.h b/src/util/unlock_guard.h
index 1ed621974..65cdccd4c 100644
--- a/src/util/unlock_guard.h
+++ b/src/util/unlock_guard.h
@@ -29,11 +29,10 @@ namespace lean {
 
    \warning The calling thread must own the lock to m_mutex
 */
-template<typename Mutex>
 class unlock_guard {
-    Mutex & m_mutex;
+    mutex & m_mutex;
 public:
-    explicit unlock_guard(Mutex & m):m_mutex(m) { m_mutex.unlock(); }
+    explicit unlock_guard(mutex & m):m_mutex(m) { m_mutex.unlock(); }
     unlock_guard(unlock_guard const &) = delete;
     unlock_guard(unlock_guard &&) = delete;
     unlock_guard & operator=(unlock_guard const &) = delete;