Index: lib/Format/ContinuationIndenter.cpp
===================================================================
--- lib/Format/ContinuationIndenter.cpp
+++ lib/Format/ContinuationIndenter.cpp
@@ -22,6 +22,9 @@
 #include "llvm/Support/Debug.h"
 
 #define DEBUG_TYPE "format-indenter"
+#define DBG(A)                                                                 \
+  llvm::dbgs() << __func__ << ":" << __LINE__ << ":" << #A << " = " << A       \
+               << "\n";
 
 namespace clang {
 namespace format {
@@ -717,6 +720,7 @@
                                                  bool DryRun) {
   FormatToken &Current = *State.NextToken;
   const FormatToken &Previous = *State.NextToken->Previous;
+  DBG(Current.TokenText);
 
   // Extra penalty that needs to be added because of the way certain line
   // breaks are chosen.
@@ -743,6 +747,13 @@
        State.Stack.back().BreakBeforeParameter))
     Penalty += Style.PenaltyBreakFirstLessLess;
 
+  // Breaking before the "{" in a text proto submessage is not desirable.
+  if (Style.Language == FormatStyle::LK_TextProto) {
+    if (Current.is(tok::l_brace)) {
+      Penalty += Style.PenaltyExcessCharacter;
+    }
+  }
+
   State.Column = getNewLineColumn(State);
 
   // Indent nested blocks relative to this column, unless in a very specific
Index: unittests/Format/FormatTestTextProto.cpp
===================================================================
--- unittests/Format/FormatTestTextProto.cpp
+++ unittests/Format/FormatTestTextProto.cpp
@@ -670,5 +670,11 @@
                "}");
 }
 
+TEST_F(FormatTestTextProto, TODO) {
+  verifyFormat("submessage: {\n"
+               "  key: 'aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa'\n"
+               "}");
+}
+
 } // end namespace tooling
 } // end namespace clang