diff --git a/prettier-tests.el b/prettier-tests.el
index 83a2848..2d33b28 100644
--- a/prettier-tests.el
+++ b/prettier-tests.el
@@ -45,6 +45,7 @@
                 (insert-file-contents original-file)
                 (setq buffer-file-name original-file)
                 (rename-buffer original-file)
+                (prettier--eval-file-if-exists "prepare.elisp")
                 (set-auto-mode)
                 (prettier--eval-file-if-exists "setup.elisp")
                 (prettier-prettify)
diff --git a/prettier.el b/prettier.el
index c3f9934..34c65d4 100644
--- a/prettier.el
+++ b/prettier.el
@@ -153,6 +153,8 @@ Requires Prettier 1.9+."
                                       html
                                       java
                                       json
+                                      json5
+                                      json-stringify
                                       less
                                       lua
                                       markdown
diff --git a/test-cases/json-stringify/a.original.json b/test-cases/json-stringify/a.original.json
new file mode 100644
index 0000000..e00f0f5
--- /dev/null
+++ b/test-cases/json-stringify/a.original.json
@@ -0,0 +1,3 @@
+{
+  "keywords": ["mtg"]
+}
diff --git a/test-cases/json-stringify/a.prettier.json b/test-cases/json-stringify/a.prettier.json
new file mode 100644
index 0000000..9d55d14
--- /dev/null
+++ b/test-cases/json-stringify/a.prettier.json
@@ -0,0 +1,5 @@
+{
+  "keywords": [
+    "mtg"
+  ]
+}
diff --git a/test-cases/json-stringify/package-lock.json b/test-cases/json-stringify/package-lock.json
new file mode 100644
index 0000000..ca025f4
--- /dev/null
+++ b/test-cases/json-stringify/package-lock.json
@@ -0,0 +1,12 @@
+{
+  "requires": true,
+  "lockfileVersion": 1,
+  "dependencies": {
+    "prettier": {
+      "version": "2.2.1",
+      "resolved": "https://registry.npmjs.org/prettier/-/prettier-2.2.1.tgz",
+      "integrity": "sha512-PqyhM2yCjg/oKkFPtTGUojv7gnZAoG80ttl45O6x2Ug/rMJw4wcc9k6aaf2hibP7BGVCCM33gZoGjyvt9mm16Q==",
+      "dev": true
+    }
+  }
+}
diff --git a/test-cases/json-stringify/package.json b/test-cases/json-stringify/package.json
new file mode 100644
index 0000000..9caf44e
--- /dev/null
+++ b/test-cases/json-stringify/package.json
@@ -0,0 +1,5 @@
+{
+  "devDependencies": {
+    "prettier": "^2.2.1"
+  }
+}
diff --git a/test-cases/json-stringify/prepare.elisp b/test-cases/json-stringify/prepare.elisp
new file mode 100644
index 0000000..c328a7c
--- /dev/null
+++ b/test-cases/json-stringify/prepare.elisp
@@ -0,0 +1,7 @@
+(progn
+  (setq buffer-file-name (concat (file-name-directory buffer-file-name) "package.json"))
+  (json-mode))
+
+;; Local Variables:
+;; mode: emacs-lisp
+;; End: