diff --git a/doc/ci/yaml/README.md b/doc/ci/yaml/README.md
index c827faace33794ac92bf67cc73708e496dca946b..5cca9d86560e5eed8e72f7782b707d5ffe8efd70 100644
--- a/doc/ci/yaml/README.md
+++ b/doc/ci/yaml/README.md
@@ -1510,7 +1510,7 @@ Possible values for `when` are:
 > [Introduced](https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/22631) in GitLab 11.5.
 
 `parallel` allows you to configure how many instances of a job to run in
-parallel. This value has to be greater than or equal to two (2).
+parallel. This value has to be greater than or equal to two (2) and less or equal than 50.
 
 This creates N instances of the same job that run in parallel. They're named
 sequentially from `job_name 1/N` to `job_name N/N`.
diff --git a/lib/gitlab/ci/config/entry/job.rb b/lib/gitlab/ci/config/entry/job.rb
index 8e8c979f973d248a34d3c5fca635eaf7d09b8e14..c8cb3248fa70ed34cef639ea694941e35a6cdcf4 100644
--- a/lib/gitlab/ci/config/entry/job.rb
+++ b/lib/gitlab/ci/config/entry/job.rb
@@ -27,7 +27,8 @@ module Gitlab
               validates :tags, array_of_strings: true
               validates :allow_failure, boolean: true
               validates :parallel, numericality: { only_integer: true,
-                                                   greater_than_or_equal_to: 2 }
+                                                   greater_than_or_equal_to: 2,
+                                                   less_than_or_equal_to: 50 }
               validates :when,
                 inclusion: { in: %w[on_success on_failure always manual delayed],
                              message: 'should be on_success, on_failure, ' \
diff --git a/spec/lib/gitlab/ci/config/entry/job_spec.rb b/spec/lib/gitlab/ci/config/entry/job_spec.rb
index ac9b0c674a5ace68119c9b2629a5165b92a553c0..57d4577a90c6d1538524cf0c5cbe1e632b23ce87 100644
--- a/spec/lib/gitlab/ci/config/entry/job_spec.rb
+++ b/spec/lib/gitlab/ci/config/entry/job_spec.rb
@@ -118,6 +118,16 @@ describe Gitlab::Ci::Config::Entry::Job do
           end
         end
 
+        context 'when it is bigger than 50' do
+          let(:config) { { parallel: 51 } }
+
+          it 'returns error about value too high' do
+            expect(entry).not_to be_valid
+            expect(entry.errors)
+              .to include 'job parallel must be less than or equal to 50'
+          end
+        end
+
         context 'when it is not an integer' do
           let(:config) { { parallel: 1.5 } }