diff --git a/lib/contentTypeParser.js b/lib/contentTypeParser.js
index a01c866dd1..474eb5bfc6 100644
--- a/lib/contentTypeParser.js
+++ b/lib/contentTypeParser.js
@@ -67,9 +67,7 @@ ContentTypeParser.prototype.add = function (contentType, opts, parserFn) {
     this.customParsers[''] = parser
   } else {
     if (contentTypeIsString) {
-      if (contentType !== 'application/json' && contentType !== 'text/plain') {
-        this.parserList.unshift(contentType)
-      }
+      this.parserList.unshift(contentType)
     } else {
       this.parserRegExpList.unshift(contentType)
     }
@@ -83,10 +81,10 @@ ContentTypeParser.prototype.hasParser = function (contentType) {
 
 ContentTypeParser.prototype.existingParser = function (contentType) {
   if (contentType === 'application/json') {
-    return this.customParsers['application/json'].fn !== this[kDefaultJsonParse]
+    return this.customParsers['application/json'] && this.customParsers['application/json'].fn !== this[kDefaultJsonParse]
   }
   if (contentType === 'text/plain') {
-    return this.customParsers['text/plain'].fn !== defaultPlainTextParser
+    return this.customParsers['text/plain'] && this.customParsers['text/plain'].fn !== defaultPlainTextParser
   }
 
   return contentType in this.customParsers
diff --git a/test/custom-parser.test.js b/test/custom-parser.test.js
index a7b467b21d..e85f3a71e7 100644
--- a/test/custom-parser.test.js
+++ b/test/custom-parser.test.js
@@ -1707,3 +1707,114 @@ test('cannot remove content type parsers after binding', t => {
     t.throws(() => fastify.removeContentTypeParser('application/json'))
   })
 })
+
+test('should be able to override the default json parser after removeAllContentTypeParsers', t => {
+  t.plan(5)
+
+  const fastify = Fastify()
+
+  fastify.post('/', (req, reply) => {
+    reply.send(req.body)
+  })
+
+  fastify.removeAllContentTypeParsers()
+
+  fastify.addContentTypeParser('application/json', function (req, payload, done) {
+    t.ok('called')
+    jsonParser(payload, function (err, body) {
+      done(err, body)
+    })
+  })
+
+  fastify.listen(0, err => {
+    t.error(err)
+
+    sget({
+      method: 'POST',
+      url: 'http://localhost:' + fastify.server.address().port,
+      body: '{"hello":"world"}',
+      headers: {
+        'Content-Type': 'application/json'
+      }
+    }, (err, response, body) => {
+      t.error(err)
+      t.equal(response.statusCode, 200)
+      t.same(body.toString(), JSON.stringify({ hello: 'world' }))
+      fastify.close()
+    })
+  })
+})
+
+test('should be able to override the default plain text parser after removeAllContentTypeParsers', t => {
+  t.plan(5)
+
+  const fastify = Fastify()
+
+  fastify.post('/', (req, reply) => {
+    reply.send(req.body)
+  })
+
+  fastify.removeAllContentTypeParsers()
+
+  fastify.addContentTypeParser('text/plain', function (req, payload, done) {
+    t.ok('called')
+    plainTextParser(payload, function (err, body) {
+      done(err, body)
+    })
+  })
+
+  fastify.listen(0, err => {
+    t.error(err)
+
+    sget({
+      method: 'POST',
+      url: 'http://localhost:' + fastify.server.address().port,
+      body: 'hello world',
+      headers: {
+        'Content-Type': 'text/plain'
+      }
+    }, (err, response, body) => {
+      t.error(err)
+      t.equal(response.statusCode, 200)
+      t.equal(body.toString(), 'hello world')
+      fastify.close()
+    })
+  })
+})
+
+test('should be able to add a custom content type parser after removeAllContentTypeParsers', t => {
+  t.plan(5)
+
+  const fastify = Fastify()
+
+  fastify.post('/', (req, reply) => {
+    reply.send(req.body)
+  })
+
+  fastify.removeAllContentTypeParsers()
+
+  fastify.addContentTypeParser('application/jsoff', function (req, payload, done) {
+    t.ok('called')
+    jsonParser(payload, function (err, body) {
+      done(err, body)
+    })
+  })
+
+  fastify.listen(0, err => {
+    t.error(err)
+
+    sget({
+      method: 'POST',
+      url: 'http://localhost:' + fastify.server.address().port,
+      body: '{"hello":"world"}',
+      headers: {
+        'Content-Type': 'application/jsoff'
+      }
+    }, (err, response, body) => {
+      t.error(err)
+      t.equal(response.statusCode, 200)
+      t.same(body.toString(), JSON.stringify({ hello: 'world' }))
+      fastify.close()
+    })
+  })
+})