diff --git a/NEWS b/NEWS
index f2f9297c9..525dac33c 100644
--- a/NEWS
+++ b/NEWS
@@ -4,6 +4,7 @@ New in spot 2.0a (not yet released)
 
   * Typo in documentation of the -H option in --help output.
   * The automaton parser would choke on comments like /******/.
+  * check_strength() should also set negated properties.
 
 New in spot 2.0 (2016-04-11)
 
diff --git a/spot/twaalgos/strength.cc b/spot/twaalgos/strength.cc
index 500addeb5..09c29b115 100644
--- a/spot/twaalgos/strength.cc
+++ b/spot/twaalgos/strength.cc
@@ -84,12 +84,11 @@ namespace spot
         delete si;
       if (set)
         {
-          if (terminal && is_term && is_weak)
-            aut->prop_terminal(true);
-          if (is_weak)
-            aut->prop_weak(true);
-          if (is_inweak)
-            aut->prop_inherently_weak(true);
+          if (terminal)
+            aut->prop_terminal(is_term && is_weak);
+          aut->prop_weak(is_weak);
+          if (inweak)
+            aut->prop_inherently_weak(is_inweak);
         }
       if (inweak)
         return is_inweak;