diff --git a/NEWS b/NEWS
index da2211029..1a309583c 100644
--- a/NEWS
+++ b/NEWS
@@ -61,6 +61,7 @@ New in spot 1.99.4a (not yet released)
   * "randaut -Q0 1" used to segfault.
   * "ltlgrind -F FILENAME/COL" did not preserve other CSV columns.
   * "ltlgrind --help" did not document FORMAT.
+  * unabbreviate could easily use forbidden operators
 
 New in spot 1.99.4 (2015-10-01)
 
diff --git a/src/tests/unabbrevwm.test b/src/tests/unabbrevwm.test
index fff7c357f..a41b9c880 100755
--- a/src/tests/unabbrevwm.test
+++ b/src/tests/unabbrevwm.test
@@ -40,7 +40,10 @@ test `uniq out | wc -l` = 1
 for i in 'GFa' 'a R b' 'a W b' 'a M b'; do
     for fg in '' F G GF; do
 	for rwm in '' R W M RW RM WM RWM; do
-	    $ltlfilt -f "$i" --unabbrev=$fg$rwm --equivalent-to "$i"
+	    $ltlfilt -f "$i" --unabbrev=$fg$rwm --equivalent-to "$i" >out
+	    test -n "$rwm" && grep "[$rwm]" out && exit 1
 	done
     done
 done
+
+true
diff --git a/src/tl/unabbrev.cc b/src/tl/unabbrev.cc
index c1a25c72c..d0bf6cd91 100644
--- a/src/tl/unabbrev.cc
+++ b/src/tl/unabbrev.cc
@@ -205,7 +205,7 @@ namespace spot
 	  auto gf2 = formula::G(f2);
 	  if (re_g_)
 	    gf2 = run(gf2);
-	  out = formula::U(f2, formula::Or({f12, out}));
+	  out = formula::U(f2, formula::Or({f12, gf2}));
 	  break;
 	}
       case op::W:
@@ -225,8 +225,8 @@ namespace spot
 	    }
 	  auto gf1 = formula::G(f1);
 	  if (re_g_)
-	    gf1 = rec(gf1);
-	  out = formula::U(f1, formula::Or({f2, out}));
+	    gf1 = run(gf1);
+	  out = formula::U(f1, formula::Or({f2, gf1}));
 	  break;
 	}
       case op::M:
diff --git a/wrap/python/tests/randltl.ipynb b/wrap/python/tests/randltl.ipynb
index dca0ebc00..7b69fe532 100644
--- a/wrap/python/tests/randltl.ipynb
+++ b/wrap/python/tests/randltl.ipynb
@@ -18,7 +18,7 @@
    "version": "3.4.3+"
   },
   "name": "",
-  "signature": "sha256:b69bb80f870979f9654dbf2c1bcc0f26f652956e1f1ea4189d5c8078caa067c6"
+  "signature": "sha256:c1de5aacd024bbec64b75f61a13e53562185c906051312d9ce5067236b7899d4"
  },
  "nbformat": 3,
  "nbformat_minor": 0,
@@ -648,13 +648,13 @@
        "text": [
         "0\n",
         "!(1 U !p1)\n",
-        "1 U ((p0 U ((p0 & p1) | (p1 R p0))) | !(1 U !((1 U !p1) & (1 U p1))))\n",
-        "1 U (!p2 U ((p0 & !p2) | (p0 R !p2)))\n",
-        "(!p1 U (((1 U !(1 U !p1)) R !p1) | (!p1 & (1 U !(1 U !p1))))) | !(1 U !(p0 | (1 U p1)))\n",
-        "X(p2 & X(p2 U (!p0 | (p2 W !p0))))\n",
+        "1 U ((p0 U ((p0 & p1) | !(1 U !p0))) | !(1 U !((1 U !p1) & (1 U p1))))\n",
+        "1 U (!p2 U ((p0 & !p2) | !(1 U p2)))\n",
+        "(!p1 U ((!p1 & (1 U !(1 U !p1))) | !(1 U p1))) | !(1 U !(p0 | (1 U p1)))\n",
+        "X(p2 & X(p2 U (!p0 | !(1 U !p2))))\n",
         "(1 U p2) | (X(!p2 | !(1 U !p2)) U ((1 U p2) U (!p1 & (1 U p2))))\n",
         "XX!(1 U !((X!p1 U (!p2 U (!p0 & !p2))) | X!(1 U !p0)))\n",
-        "XX(1 U (p1 U ((p0 & p1) | (p0 R p1))))\n",
+        "XX(1 U (p1 U ((p0 & p1) | !(1 U !p1))))\n",
         "p2 & Xp0\n"
        ]
       }