Index: lib/Format/ContinuationIndenter.cpp
===================================================================
--- lib/Format/ContinuationIndenter.cpp
+++ lib/Format/ContinuationIndenter.cpp
@@ -597,7 +597,9 @@
             TT_AttributeParen, TT_FunctionAnnotationRParen, TT_JavaAnnotation,
             TT_LeadingJavaAnnotation))) ||
       (!Style.IndentWrappedFunctionNames &&
-       NextNonComment->isOneOf(tok::kw_operator, TT_FunctionDeclarationName)))
+       (NextNonComment->is(TT_FunctionDeclarationName) ||
+        (NextNonComment->is(tok::kw_operator) &&
+         !NextNonComment->Previous->is(tok::coloncolon)))))
     return std::max(State.Stack.back().LastSpace, State.Stack.back().Indent);
   if (NextNonComment->is(TT_SelectorName)) {
     if (!State.Stack.back().ObjCSelectorNameFound) {
Index: unittests/Format/FormatTest.cpp
===================================================================
--- unittests/Format/FormatTest.cpp
+++ unittests/Format/FormatTest.cpp
@@ -3707,6 +3707,11 @@
       "SomeClasssssssssssssssssssssssssssssssssssssss::\n"
       "    bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb(Cccccccccccccc cccccccccc);",
       getGoogleStyle());
+  verifyFormat(
+      "Aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\n"
+      "SomeClasssssssssssssssssssssssssssssssssssssssssssssssssssssssssssss::\n"
+      "    operator+=(Cccccccccccccc cccccccccc);",
+      getGoogleStyle());
 
   // However, there are exceptions, if a sufficient amount of lines can be
   // saved.