diff --git a/lib/readthis/serializers.rb b/lib/readthis/serializers.rb
index 5b31f4a..d589515 100644
--- a/lib/readthis/serializers.rb
+++ b/lib/readthis/serializers.rb
@@ -41,7 +41,7 @@ def <<(serializer)
       case
       when serializers.frozen?
         raise SerializersFrozenError
-      when serializers.length > SERIALIZER_LIMIT
+      when serializers.length >= SERIALIZER_LIMIT
         raise SerializersLimitError
       else
         @serializers[serializer] = flags.max.succ
diff --git a/spec/readthis/serializers_spec.rb b/spec/readthis/serializers_spec.rb
index c5213a5..eff269a 100644
--- a/spec/readthis/serializers_spec.rb
+++ b/spec/readthis/serializers_spec.rb
@@ -22,9 +22,9 @@
 
     it 'prevents more than seven serializers' do
       serializers = Readthis::Serializers.new
-
+      serializers << Class.new until serializers.flags.length >= 7
       expect do
-        10.times { serializers << Class.new }
+        serializers << Class.new
       end.to raise_error(Readthis::SerializersLimitError)
     end
   end