diff --git a/Adapter.cc b/Adapter.cc
index 6f1df95..aa5bdb3 100644
--- a/Adapter.cc
+++ b/Adapter.cc
@@ -147,7 +147,13 @@ namespace pEp {
 
         bool in_shutdown()
         {
-            SYNC_EVENT ev = q.back();
+            SYNC_EVENT ev;
+            try {
+                ev = q.back();
+            }
+            catch (std::underflow_error&) {
+                return false;
+            }
             if (ev)
                 return false;
             else
diff --git a/locked_queue.hh b/locked_queue.hh
index b390799..e96faac 100644
--- a/locked_queue.hh
+++ b/locked_queue.hh
@@ -38,17 +38,21 @@ namespace utility
             _q.clear();
         }
 
-        // undefined behavior when queue empty
+        // defined behavior when queue empty
         T back()
         {
             Lock lg(_mtx);
+            if (_q.empty())
+                throw std::underflow_error("queue empty");
             return _q.back();
         }
 
-        // undefined behavior when queue empty
+        // defined behavior when queue empty
         T front()
         {
             Lock lg(_mtx);
+            if (_q.empty())
+                throw std::underflow_error("queue empty");
             return _q.front();
         }