diff --git a/spot/twa/acc.hh b/spot/twa/acc.hh
index 6ddde3ef8..6192e9dba 100644
--- a/spot/twa/acc.hh
+++ b/spot/twa/acc.hh
@@ -102,7 +102,10 @@ namespace spot
         : mark_t(_value_t::zero())
       {
         for (iterator i = begin; i != end; ++i)
-          set(*i);
+          if (SPOT_LIKELY(*i < SPOT_MAX_ACCSETS))
+            set(*i);
+          else
+            report_too_many_sets();
       }
 
       /// Create a mark_t from a list of set numbers.
diff --git a/tests/core/acc.cc b/tests/core/acc.cc
index 91e829724..74c32fa49 100644
--- a/tests/core/acc.cc
+++ b/tests/core/acc.cc
@@ -53,6 +53,17 @@ static void print(const std::vector<std::vector<int>>& res)
     }
 }
 
+static void expect(const std::exception& e, const char* prefix)
+{
+  if (std::strncmp(e.what(), "Too many acceptance sets used.",
+                   strlen(prefix)))
+    {
+      std::cerr << "exception: " << e.what() << '\n';
+      std::cerr << "expected:  " << prefix << '\n';
+      abort();
+    }
+}
+
 int main()
 {
   spot::acc_cond ac(4);
@@ -189,7 +200,7 @@ int main()
     }
   catch (const std::runtime_error& e)
     {
-      assert(!std::strncmp(e.what(), "Too many acceptance sets used.", 30));
+      expect(e, "Too many acceptance sets used.");
     }
 
 #if SPOT_DEBUG
@@ -204,7 +215,7 @@ int main()
     }
   catch (const std::runtime_error& e)
     {
-      assert(!std::strncmp(e.what(), "Too many acceptance sets used.", 30));
+      expect(e, "Too many acceptance sets used.");
     }
 
   try
@@ -214,17 +225,17 @@ int main()
     }
   catch (const std::runtime_error& e)
     {
-      assert(!std::strncmp(e.what(), "Too many acceptance sets used.", 30));
+      expect(e, "Too many acceptance sets used.");
     }
+#endif
   try
     {
       spot::acc_cond::mark_t m{spot::acc_cond::mark_t::max_accsets()};
     }
   catch (const std::runtime_error& e)
     {
-      assert(!std::strcmp(e.what(), "bit index is out of bounds"));
+      expect(e, "Too many acceptance sets used.");
     }
-#endif
 
   return 0;
 }
diff --git a/tests/python/except.py b/tests/python/except.py
index 598d70b6a..f4ece980b 100644
--- a/tests/python/except.py
+++ b/tests/python/except.py
@@ -169,7 +169,7 @@ else:
 try:
     m = spot.mark_t([0, n, 1])
 except RuntimeError as e:
-    assert "bit index is out of bounds" in str(e)
+    assert "Too many acceptance sets used.  The limit is" in str(e)
 else:
     report_missing_exception()