Index: unittests/Format/FormatTestProto.cpp
===================================================================
--- unittests/Format/FormatTestProto.cpp
+++ unittests/Format/FormatTestProto.cpp
@@ -61,6 +61,10 @@
                "      really.really.long.qualified.type.aaa.aaaaaaa.aaaaaaaa\n"
                "          another_fiiiiiiiiiiiiiiiiiiiiield = 2;\n"
                "}");
+  verifyFormat("message SomeMessage {\n"
+               "  map<string, Project> projects = 1;\n"
+               "  optional map<string, int32> size_projects = 2;\n"
+               "}");
 }
 
 TEST_F(FormatTestProto, KeywordsInOtherLanguages) {