Index: lib/Format/TokenAnnotator.cpp
===================================================================
--- lib/Format/TokenAnnotator.cpp
+++ lib/Format/TokenAnnotator.cpp
@@ -759,6 +759,9 @@
         Tok->Type = TT_BinaryOperator;
       break;
     case tok::kw_operator:
+      if (Style.Language == FormatStyle::LK_TextProto ||
+          Style.Language == FormatStyle::LK_Proto)
+        break;
       while (CurrentToken &&
              !CurrentToken->isOneOf(tok::l_paren, tok::semi, tok::r_paren)) {
         if (CurrentToken->isOneOf(tok::star, tok::amp))
Index: unittests/Format/FormatTestProto.cpp
===================================================================
--- unittests/Format/FormatTestProto.cpp
+++ unittests/Format/FormatTestProto.cpp
@@ -478,5 +478,17 @@
                "};");
 }
 
+TEST_F(FormatTestProto, AcceptsOperatorAsKeyInOptions) {
+  verifyFormat("option (MyProto.options) = {\n"
+               "  bbbbbbbbb: <\n"
+               "    ccccccccccccccccccccccc: <\n"
+               "      operator: 1\n"
+               "      operator: 2\n"
+               "      operator { key: value }\n"
+               "    >\n"
+               "  >\n"
+               "};");
+}
+
 } // end namespace tooling
 } // end namespace clang
Index: unittests/Format/FormatTestTextProto.cpp
===================================================================
--- unittests/Format/FormatTestTextProto.cpp
+++ unittests/Format/FormatTestTextProto.cpp
@@ -440,5 +440,17 @@
   Style.Cpp11BracedListStyle = true;
   verifyFormat("keys: [1]", Style);
 }
+
+TEST_F(FormatTestTextProto, AcceptsOperatorAsKey) {
+  verifyFormat("aaaaaaaaaaa: <\n"
+               "  bbbbbbbbb: <\n"
+               "    ccccccccccccccccccccccc: <\n"
+               "      operator: 1\n"
+               "      operator: 2\n"
+               "      operator { key: value }\n"
+               "    >\n"
+               "  >\n"
+               ">");
+}
 } // end namespace tooling
 } // end namespace clang