diff --git a/workspaces/arborist/lib/arborist/build-ideal-tree.js b/workspaces/arborist/lib/arborist/build-ideal-tree.js
index 899d92ca937cc..dffcd546b8677 100644
--- a/workspaces/arborist/lib/arborist/build-ideal-tree.js
+++ b/workspaces/arborist/lib/arborist/build-ideal-tree.js
@@ -176,7 +176,7 @@ module.exports = cls => class IdealTreeBuilder extends cls {
   // public method
   async buildIdealTree (options = {}) {
     if (this.idealTree) {
-      return Promise.resolve(this.idealTree)
+      return this.idealTree
     }
 
     // allow the user to set reify options on the ctor as well.
@@ -194,8 +194,7 @@ module.exports = cls => class IdealTreeBuilder extends cls {
     process.emit('time', 'idealTree')
 
     if (!options.add && !options.rm && !options.update && this[_global]) {
-      const er = new Error('global requires add, rm, or update option')
-      return Promise.reject(er)
+      throw new Error('global requires add, rm, or update option')
     }
 
     // first get the virtual tree, if possible.  If there's a lockfile, then
@@ -334,6 +333,7 @@ module.exports = cls => class IdealTreeBuilder extends cls {
             root.meta.lockfileVersion = defaultLockfileVersion
           }
         }
+        root.meta.inferFormattingOptions(root.package)
         return root
       })
 
diff --git a/workspaces/arborist/lib/shrinkwrap.js b/workspaces/arborist/lib/shrinkwrap.js
index a7a68c98c6d6d..b45fea0ac6111 100644
--- a/workspaces/arborist/lib/shrinkwrap.js
+++ b/workspaces/arborist/lib/shrinkwrap.js
@@ -424,6 +424,18 @@ class Shrinkwrap {
       .map(fn => fn && maybeStatFile(fn)))
   }
 
+  inferFormattingOptions (packageJSONData) {
+    // don't use detect-indent, just pick the first line.
+    // if the file starts with {" then we have an indent of '', ie, none
+    // which will default to 2 at save time.
+    const {
+      [Symbol.for('indent')]: indent,
+      [Symbol.for('newline')]: newline,
+    } = packageJSONData
+    this.indent = indent !== undefined ? indent : this.indent
+    this.newline = newline !== undefined ? newline : this.newline
+  }
+
   load () {
     // we don't need to load package-lock.json except for top of tree nodes,
     // only npm-shrinkwrap.json.
@@ -451,15 +463,7 @@ class Shrinkwrap {
 
       return data ? parseJSON(data) : {}
     }).then(async data => {
-      // don't use detect-indent, just pick the first line.
-      // if the file starts with {" then we have an indent of '', ie, none
-      // which will default to 2 at save time.
-      const {
-        [Symbol.for('indent')]: indent,
-        [Symbol.for('newline')]: newline,
-      } = data
-      this.indent = indent !== undefined ? indent : this.indent
-      this.newline = newline !== undefined ? newline : this.newline
+      this.inferFormattingOptions(data)
 
       if (!this.hiddenLockfile || !data.packages) {
         return data
diff --git a/workspaces/arborist/tap-snapshots/test/arborist/build-ideal-tree.js.test.cjs b/workspaces/arborist/tap-snapshots/test/arborist/build-ideal-tree.js.test.cjs
index ca47bbbe1b135..d8f4fc4d52b1e 100644
--- a/workspaces/arborist/tap-snapshots/test/arborist/build-ideal-tree.js.test.cjs
+++ b/workspaces/arborist/tap-snapshots/test/arborist/build-ideal-tree.js.test.cjs
@@ -97673,6 +97673,37 @@ ArboristNode {
 }
 `
 
+exports[`test/arborist/build-ideal-tree.js TAP store files with a custom indenting > must match snapshot 1`] = `
+{
+	"name": "tab-indented-package-json",
+	"version": "1.0.0",
+	"lockfileVersion": 2,
+	"requires": true,
+	"packages": {
+		"": {
+			"name": "tab-indented-package-json",
+			"version": "1.0.0",
+			"dependencies": {
+				"abbrev": "^1.0.0"
+			}
+		},
+		"node_modules/abbrev": {
+			"version": "1.1.1",
+			"resolved": "https://registry.npmjs.org/abbrev/-/abbrev-1.1.1.tgz",
+			"integrity": "sha512-nne9/IiQ/hzIhY6pdDnbBtz7DjPTKrY00P/zvPSm5pOFkl6xuGrGnXn/VtTNNfNtAfZ9/1RtehkszU9qcTii0Q=="
+		}
+	},
+	"dependencies": {
+		"abbrev": {
+			"version": "1.1.1",
+			"resolved": "https://registry.npmjs.org/abbrev/-/abbrev-1.1.1.tgz",
+			"integrity": "sha512-nne9/IiQ/hzIhY6pdDnbBtz7DjPTKrY00P/zvPSm5pOFkl6xuGrGnXn/VtTNNfNtAfZ9/1RtehkszU9qcTii0Q=="
+		}
+	}
+}
+
+`
+
 exports[`test/arborist/build-ideal-tree.js TAP tap vs react15 > build ideal tree with tap collision 1`] = `
 ArboristNode {
   "children": Map {
diff --git a/workspaces/arborist/test/arborist/build-ideal-tree.js b/workspaces/arborist/test/arborist/build-ideal-tree.js
index 80db25880e46c..8ec8dab914e35 100644
--- a/workspaces/arborist/test/arborist/build-ideal-tree.js
+++ b/workspaces/arborist/test/arborist/build-ideal-tree.js
@@ -3682,3 +3682,16 @@ t.test('overrides', t => {
 
   t.end()
 })
+
+t.test('store files with a custom indenting', async t => {
+  const tabIndentedPackageJson =
+    fs.readFileSync(
+      resolve(__dirname, '../fixtures/tab-indented-package-json/package.json'),
+      'utf8'
+    ).replace(/\r\n/g, '\n')
+  const path = t.testdir({
+    'package.json': tabIndentedPackageJson,
+  })
+  const tree = await buildIdeal(path)
+  t.matchSnapshot(String(tree.meta))
+})