diff --git a/applicationset/generators/pull_request.go b/applicationset/generators/pull_request.go
index 287a00be1ae81..9bb7f162e314f 100644
--- a/applicationset/generators/pull_request.go
+++ b/applicationset/generators/pull_request.go
@@ -7,6 +7,7 @@ import (
 	"time"
 
 	corev1 "k8s.io/api/core/v1"
+	"k8s.io/apimachinery/pkg/util/validation"
 	"sigs.k8s.io/controller-runtime/pkg/client"
 
 	"github.com/gosimple/slug"
@@ -73,10 +74,10 @@ func (g *PullRequestGenerator) GenerateParams(appSetGenerator *argoprojiov1alpha
 	params := make([]map[string]interface{}, 0, len(pulls))
 
 	// In order to follow the DNS label standard as defined in RFC 1123,
-	// we need to limit the 'branch' to 50 to give room to append/suffix-ing it
-	// with 13 more characters. Also, there is the need to clean it as recommended
+	// we need to limit the 'branch' to 63.
+	// Also, there is the need to clean it as recommended
 	// here https://kubernetes.io/docs/concepts/overview/working-with-objects/names/#dns-label-names
-	slug.MaxLength = 50
+	slug.MaxLength = 63
 
 	// Converting underscores to dashes
 	slug.CustomSub = map[string]string{
@@ -90,10 +91,16 @@ func (g *PullRequestGenerator) GenerateParams(appSetGenerator *argoprojiov1alpha
 			shortSHALength = len(pull.HeadSHA)
 		}
 
+		branchSlug := slug.Make(pull.Branch)
+		errors := validation.IsDNS1123Label(branchSlug)
+		if len(errors) > 0 {
+			return nil, fmt.Errorf("invalid branch slug: %v for branch %v: %v", branchSlug, pull.Branch, errors)
+		}
+
 		params = append(params, map[string]interface{}{
 			"number":         strconv.Itoa(pull.Number),
 			"branch":         pull.Branch,
-			"branch_slug":    slug.Make(pull.Branch),
+			"branch_slug":    branchSlug,
 			"head_sha":       pull.HeadSHA,
 			"head_short_sha": pull.HeadSHA[:shortSHALength],
 		})
diff --git a/applicationset/generators/pull_request_test.go b/applicationset/generators/pull_request_test.go
index ef969376d9719..82040d8b3377a 100644
--- a/applicationset/generators/pull_request_test.go
+++ b/applicationset/generators/pull_request_test.go
@@ -64,13 +64,38 @@ func TestPullRequestGithubGenerateParams(t *testing.T) {
 				{
 					"number":         "2",
 					"branch":         "feat/areally+long_pull_request_name_to_test_argo_slugification_and_branch_name_shortening_feature",
-					"branch_slug":    "feat-areally-long-pull-request-name-to-test-argo",
+					"branch_slug":    "feat-areally-long-pull-request-name-to-test-argo-slugification",
 					"head_sha":       "9b34ff5bd418e57d58891eb0aa0728043ca1e8be",
 					"head_short_sha": "9b34ff5b",
 				},
 			},
 			expectedErr: nil,
 		},
+		{
+			selectFunc: func(context.Context, *argoprojiov1alpha1.PullRequestGenerator, *argoprojiov1alpha1.ApplicationSet) (pullrequest.PullRequestService, error) {
+				return pullrequest.NewFakeService(
+					ctx,
+					[]*pullrequest.PullRequest{
+						&pullrequest.PullRequest{
+							Number:  2,
+							Branch:  "abdominoposterior-pneumonoultramicroscopicsilicovolcanoconiosis-longest-branch-name",
+							HeadSHA: "09ae444a85e105b34abd0f15dbde72938580f970",
+						},
+					},
+					nil,
+				)
+			},
+			expected: []map[string]interface{}{
+				{
+					"number":         "2",
+					"branch":         "abdominoposterior-pneumonoultramicroscopicsilicovolcanoconiosis-longest-branch-name",
+					"branch_slug":    "abdominoposterior-pneumonoultramicroscopicsilicovolcanoconiosis",
+					"head_sha":       "09ae444a85e105b34abd0f15dbde72938580f970",
+					"head_short_sha": "09ae444a",
+				},
+			},
+			expectedErr: nil,
+		},
 		{
 			selectFunc: func(context.Context, *argoprojiov1alpha1.PullRequestGenerator, *argoprojiov1alpha1.ApplicationSet) (pullrequest.PullRequestService, error) {
 				return pullrequest.NewFakeService(
diff --git a/docs/operator-manual/applicationset/Generators-Pull-Request.md b/docs/operator-manual/applicationset/Generators-Pull-Request.md
index de5866aaf00a8..924c8ef631204 100644
--- a/docs/operator-manual/applicationset/Generators-Pull-Request.md
+++ b/docs/operator-manual/applicationset/Generators-Pull-Request.md
@@ -268,7 +268,7 @@ spec:
 
 * `number`: The ID number of the pull request.
 * `branch`: The name of the branch of the pull request head.
-* `branch_slug`: The branch name will be cleaned to be conform to the DNS label standard as defined in [RFC 1123](https://kubernetes.io/docs/concepts/overview/working-with-objects/names/#dns-label-names), and truncated to 50 characters to give room to append/suffix-ing it with 13 more characters.
+* `branch_slug`: The branch name will be cleaned to be conform to the DNS label standard as defined in [RFC 1123](https://kubernetes.io/docs/concepts/overview/working-with-objects/names/#dns-label-names).
 * `head_sha`: This is the SHA of the head of the pull request.
 * `head_short_sha`: This is the short SHA of the head of the pull request (8 characters long or the length of the head SHA if it's shorter).