diff --git a/clang/include/clang/Tooling/Refactoring/Transformer.h b/clang/include/clang/Tooling/Refactoring/Transformer.h
--- a/clang/include/clang/Tooling/Refactoring/Transformer.h
+++ b/clang/include/clang/Tooling/Refactoring/Transformer.h
@@ -44,12 +44,18 @@
   Name,
 };
 
-using TextGenerator =
-    std::function<std::string(const ast_matchers::MatchFinder::MatchResult &)>;
-
-/// Wraps a string as a TextGenerator.
+// \c TextGenerator may fail because it processes dynamically-bound match
+// results. For example, a typo in the name of a bound node can lead to a
+// failure in the string generation code. We prefer to return \c Expected rather
+// than assert on such failures to allow this code to be run in a variety of
+// settings (including servers).
+using TextGenerator = std::function<Expected<std::string>(
+    const ast_matchers::MatchFinder::MatchResult &)>;
+
+/// Wraps a string as a (trivially successful) TextGenerator.
 inline TextGenerator text(std::string M) {
-  return [M](const ast_matchers::MatchFinder::MatchResult &) { return M; };
+  return [M](const ast_matchers::MatchFinder::MatchResult &)
+             -> Expected<std::string> { return M; };
 }
 
 // Description of a source-code edit, expressed in terms of an AST node.
diff --git a/clang/lib/Tooling/Refactoring/Transformer.cpp b/clang/lib/Tooling/Refactoring/Transformer.cpp
--- a/clang/lib/Tooling/Refactoring/Transformer.cpp
+++ b/clang/lib/Tooling/Refactoring/Transformer.cpp
@@ -157,12 +157,16 @@
         Edit.Target, It->second, Edit.Kind, Edit.Part, *Result.Context);
     if (auto Err = RangeOrErr.takeError())
       return std::move(Err);
-    Transformation T;
-    T.Range = *RangeOrErr;
-    if (T.Range.isInvalid() ||
-        isOriginMacroBody(*Result.SourceManager, T.Range.getBegin()))
+    auto &Range = *RangeOrErr;
+    if (Range.isInvalid() ||
+        isOriginMacroBody(*Result.SourceManager, Range.getBegin()))
       return SmallVector<Transformation, 0>();
-    T.Replacement = Edit.Replacement(Result);
+    auto ReplacementOrErr = Edit.Replacement(Result);
+    if (auto Err = ReplacementOrErr.takeError())
+      return std::move(Err);
+    Transformation T;
+    T.Range = Range;
+    T.Replacement = std::move(*ReplacementOrErr);
     Transformations.push_back(std::move(T));
   }
   return Transformations;