diff --git a/src/doc/doc-utils.js b/src/doc/doc-utils.js
index 656617a13a42..f27f4d762e5c 100644
--- a/src/doc/doc-utils.js
+++ b/src/doc/doc-utils.js
@@ -72,6 +72,21 @@ function mapDoc(doc, cb) {
   return cb(doc);
 }
 
+function mapDocInPlace(doc, cb) {
+  if (doc.type === "concat" || doc.type === "fill") {
+    for (let partIndex = 0; partIndex < doc.parts.length; ++partIndex) {
+      doc.parts[partIndex] = mapDocInPlace(doc.parts[partIndex], cb);
+    }
+  } else if (doc.type === "if-break") {
+    doc.breakContents =
+      doc.breakContents && mapDocInPlace(doc.breakContents, cb);
+    doc.flatContents = doc.flatContents && mapDocInPlace(doc.flatContents, cb);
+  } else if (doc.contents) {
+    doc.contents = mapDocInPlace(doc.contents, cb);
+  }
+  return cb(doc);
+}
+
 function findInDoc(doc, fn, defaultValue) {
   let result = defaultValue;
   let hasStopped = false;
@@ -212,6 +227,7 @@ module.exports = {
   traverseDoc,
   findInDoc,
   mapDoc,
+  mapDocInPlace,
   propagateBreaks,
   removeLines,
   stripTrailingHardline
diff --git a/src/language-js/embed.js b/src/language-js/embed.js
index eb3e1e9d3666..b122613de3bf 100644
--- a/src/language-js/embed.js
+++ b/src/language-js/embed.js
@@ -13,7 +13,7 @@ const {
     group,
     dedentToRoot
   },
-  utils: { mapDoc, stripTrailingHardline }
+  utils: { mapDoc, mapDocInPlace, stripTrailingHardline }
 } = require("../doc");
 
 function embed(path, print, textToDoc, options) {
@@ -207,8 +207,10 @@ function uncook(cookedValue) {
   return cookedValue.replace(/([\\`]|\$\{)/g, "\\$1");
 }
 
+// Note that this uses mapDocInPlace, and so modifies the
+// original doc object.
 function escapeTemplateCharacters(doc, raw) {
-  return mapDoc(doc, currentDoc => {
+  return mapDocInPlace(doc, currentDoc => {
     if (!currentDoc.parts) {
       return currentDoc;
     }
diff --git a/src/main/core.js b/src/main/core.js
index 0f37afe6ae2b..4331dd43128d 100644
--- a/src/main/core.js
+++ b/src/main/core.js
@@ -14,7 +14,7 @@ const {
 const rangeUtil = require("./range-util");
 const privateUtil = require("../common/util");
 const {
-  utils: { mapDoc },
+  utils: { mapDocInPlace },
   printer: { printDocToString },
   debug: { printDocToDebug }
 } = require("../doc");
@@ -89,7 +89,7 @@ function coreFormat(text, opts, addAlignmentSize) {
   const result = printDocToString(
     opts.endOfLine === "lf"
       ? doc
-      : mapDoc(doc, currentDoc =>
+      : mapDocInPlace(doc, currentDoc =>
           typeof currentDoc === "string" && currentDoc.indexOf("\n") !== -1
             ? currentDoc.replace(/\n/g, eol)
             : currentDoc