diff --git a/client.h b/client.h
index 429c4f7f02..5218b9b75a 100644
--- a/client.h
+++ b/client.h
@@ -709,6 +709,7 @@ inline
 Time Client::userTime() const
     {
     assert( user_time != CurrentTime );
+    assert( user_time != -1U );
     return user_time;
     }
 
diff --git a/manage.cpp b/manage.cpp
index ae050f8aad..02f7ef47b4 100644
--- a/manage.cpp
+++ b/manage.cpp
@@ -474,8 +474,12 @@ bool Client::manage( Window w, bool isMapped )
     if( isTopMenu())
         hideClient( true );
 
-    if( user_time == CurrentTime ) // no known user time, set something old
+    if( user_time == CurrentTime || user_time == -1U ) // no known user time, set something old
+        {
         user_time = qt_x_time - 1000000;
+        if( user_time == CurrentTime || user_time == -1U ) // let's be paranoid
+            user_time = qt_x_time - 1000000 + 10;
+        }
 
     updateWorkareaDiffs( area );