diff --git a/clang/lib/Format/ContinuationIndenter.cpp b/clang/lib/Format/ContinuationIndenter.cpp
--- a/clang/lib/Format/ContinuationIndenter.cpp
+++ b/clang/lib/Format/ContinuationIndenter.cpp
@@ -1651,7 +1651,7 @@
   StringRef OldDelimiter = *getRawStringDelimiter(Current.TokenText);
   StringRef NewDelimiter =
       getCanonicalRawStringDelimiter(Style, RawStringStyle.Language);
-  if (NewDelimiter.empty() || OldDelimiter.empty())
+  if (NewDelimiter.empty())
     NewDelimiter = OldDelimiter;
   // The text of a raw string is between the leading 'R"delimiter(' and the
   // trailing 'delimiter)"'.
diff --git a/clang/lib/Format/Format.cpp b/clang/lib/Format/Format.cpp
--- a/clang/lib/Format/Format.cpp
+++ b/clang/lib/Format/Format.cpp
@@ -1137,7 +1137,7 @@
               "ParseTestProto",
               "ParsePartialTestProto",
           },
-          /*CanonicalDelimiter=*/"",
+          /*CanonicalDelimiter=*/"pb",
           /*BasedOnStyle=*/"google",
       },
   };
diff --git a/clang/unittests/Format/FormatTestRawStrings.cpp b/clang/unittests/Format/FormatTestRawStrings.cpp
--- a/clang/unittests/Format/FormatTestRawStrings.cpp
+++ b/clang/unittests/Format/FormatTestRawStrings.cpp
@@ -782,11 +782,16 @@
 }
 
 TEST_F(FormatTestRawStrings, UpdatesToCanonicalDelimiters) {
-  FormatStyle Style = getRawStringPbStyleWithColumns(25);
+  FormatStyle Style = getRawStringPbStyleWithColumns(35);
   Style.RawStringFormats[0].CanonicalDelimiter = "proto";
+  Style.RawStringFormats[0].EnclosingFunctions.push_back("PARSE_TEXT_PROTO");
+
   expect_eq(R"test(a = R"proto(key: value)proto";)test",
             format(R"test(a = R"pb(key:value)pb";)test", Style));
 
+  expect_eq(R"test(PARSE_TEXT_PROTO(R"proto(key: value)proto");)test",
+            format(R"test(PARSE_TEXT_PROTO(R"(key:value)");)test", Style));
+
   // Don't update to canonical delimiter if it occurs as a raw string suffix in
   // the raw string content.
   expect_eq(R"test(a = R"pb(key: ")proto")pb";)test",