diff --git a/src/tgbaalgos/lbtt.cc b/src/tgbaalgos/lbtt.cc
index a86c47e3a..bc65d2048 100644
--- a/src/tgbaalgos/lbtt.cc
+++ b/src/tgbaalgos/lbtt.cc
@@ -169,9 +169,7 @@ namespace spot
 	const ltl::formula* af = acc_f[n] = envacc.require(s.str());
 	aut->declare_acceptance_condition(af->clone());
       }
-    std::vector<bdd> acc_b(num_acc);
-    for (unsigned n = 0; n < num_acc; ++n)
-      acc_b[n] = aut->get_acceptance_condition(acc_f[n]);
+    std::map<int, bdd> acc_b;
 
     for (unsigned n = 0; n < num_states; ++n)
       {
@@ -197,13 +195,25 @@ namespace spot
 		is >> acc_n;
 		if (acc_n == -1)
 		  break;
-		if (acc_n < 0 || (unsigned)acc_n >= num_acc)
+		std::map<int, bdd>::const_iterator i = acc_b.find(acc_n);
+		if (i != acc_b.end())
 		  {
-		    error += "invalid acceptance set";
-		    goto fail;
+		    acc |= i->second;
+		  }
+		else
+		  {
+		    size_t s = acc_b.size();
+		    if (s >= num_acc)
+		      {
+			error += "more acceptance sets used than declared";
+			goto fail;
+		      }
+		    bdd a = aut->get_acceptance_condition(acc_f[s]);
+		    acc_b[acc_n] = a;
+		    acc |= a;
 		  }
-		acc |= acc_b[acc_n];
 	      }
+
 	    std::string guard;
 	    std::getline(is, guard);
 	    ltl::parse_error_list pel;
@@ -242,9 +252,7 @@ namespace spot
 	const ltl::formula* af = acc_f[n] = envacc.require(s.str());
 	aut->declare_acceptance_condition(af->clone());
       }
-    std::vector<bdd> acc_b(num_acc);
-    for (unsigned n = 0; n < num_acc; ++n)
-      acc_b[n] = aut->get_acceptance_condition(acc_f[n]);
+    std::map<int, bdd> acc_b;
 
     for (unsigned n = 0; n < num_states; ++n)
       {
@@ -262,12 +270,23 @@ namespace spot
 	    is >> acc_n;
 	    if (acc_n == -1)
 	      break;
-	    if (acc_n < 0 || (unsigned)acc_n >= num_acc)
+	    std::map<int, bdd>::const_iterator i = acc_b.find(acc_n);
+	    if (i != acc_b.end())
 	      {
-		error += "invalid acceptance set";
-		goto fail;
+		acc |= i->second;
+	      }
+	    else
+	      {
+		size_t s = acc_b.size();
+		if (s >= num_acc)
+		  {
+		    error += "more acceptance sets used than declared";
+		    goto fail;
+		  }
+		bdd a = aut->get_acceptance_condition(acc_f[s]);
+		acc_b[acc_n] = a;
+		acc |= a;
 	      }
-	    acc |= acc_b[acc_n];
 	  }
 
 	// Read the transitions.
diff --git a/src/tgbatest/lbttparse.test b/src/tgbatest/lbttparse.test
index 6f3970619..ff552e94b 100755
--- a/src/tgbatest/lbttparse.test
+++ b/src/tgbatest/lbttparse.test
@@ -81,3 +81,21 @@ run 0 ../ltl2tgba -ks -XL wring2lbtt > size
 test "`cat size | sed -n 's/states: //p'`" = 4
 test "`cat size | sed -n 's/transitions: //p'`" = 6
 
+# Another example from wring2lbtt (or modella), showing that the
+# acceptance set of the state is not always numbered from 0.
+cat >wring2lbtt2 <<EOF
+6 1 0 1 -1 1 | & ! p0 ! p1 & p0 ! p1
+2 & ! p0 ! p1
+3 | & p0 p1 & ! p0 p1
+-1 1 0 -1 4 ! p1
+-1 2 0 -1 2 & ! p0 ! p1
+3 | & p0 p1 & ! p0 p1
+-1 3 0 -1 5 t
+-1 4 0 1 -1 4 ! p1
+-1 5 0 1 -1 5 t
+-1
+EOF
+
+run 0 ../ltl2tgba -ks -XL wring2lbtt2 > size
+test "`cat size | sed -n 's/states: //p'`" = 6
+test "`cat size | sed -n 's/transitions: //p'`" = 9