diff --git a/lib/tjson/datatype/timestamp.rb b/lib/tjson/datatype/timestamp.rb
index aa704f4..55de468 100644
--- a/lib/tjson/datatype/timestamp.rb
+++ b/lib/tjson/datatype/timestamp.rb
@@ -10,7 +10,9 @@ def tag
 
       def convert(str)
         raise TJSON::TypeError, "expected String, got #{str.class}: #{str.inspect}" unless str.is_a?(::String)
-        raise TJSON::ParseError, "invalid timestamp: #{str.inspect}" unless str =~ /\A\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}Z\z/
+        unless str =~ /\A\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(\.\d+)?Z\z/
+          raise TJSON::ParseError, "invalid timestamp: #{str.inspect}"
+        end
 
         ::Time.iso8601(str)
       end
diff --git a/spec/tjson/datatype/timestamp_spec.rb b/spec/tjson/datatype/timestamp_spec.rb
index 0f6d796..dd440d2 100644
--- a/spec/tjson/datatype/timestamp_spec.rb
+++ b/spec/tjson/datatype/timestamp_spec.rb
@@ -16,4 +16,20 @@
       expect { subject.convert(invalid_timestamp) }.to raise_error(TJSON::ParseError)
     end
   end
+
+  context "valid UTC RFC3339 timestamp with fractional seconds" do
+    let(:example_timestamp) { "2016-10-02T07:31:51.42Z" }
+
+    it "parses successfully" do
+      expect(subject.convert(example_timestamp)).to be_a Time
+    end
+  end
+
+  context "valid UTC RFC3339 timestamp with comma separated fractional seconds" do
+    let(:invalid_timestamp) { "2016-10-02T07:31:51,42Z" }
+
+    it "raises TJSON::ParseError" do
+      expect { subject.convert(invalid_timestamp) }.to raise_error(TJSON::ParseError)
+    end
+  end
 end