diff --git a/src/main/java/io/jenkins/plugins/gitlabbranchsource/GitLabMergeRequestCommentTrigger.java b/src/main/java/io/jenkins/plugins/gitlabbranchsource/GitLabMergeRequestCommentTrigger.java
index eedd8783..46a02855 100644
--- a/src/main/java/io/jenkins/plugins/gitlabbranchsource/GitLabMergeRequestCommentTrigger.java
+++ b/src/main/java/io/jenkins/plugins/gitlabbranchsource/GitLabMergeRequestCommentTrigger.java
@@ -52,8 +52,10 @@ public void isMatch() {
                         if (!sourceContext.mrCommentTriggerEnabled()) {
                             continue;
                         }
-                        if (gitLabSCMSource.getProjectId()
-                                        == getPayload().getMergeRequest().getTargetProjectId()
+                        Long projectId = gitLabSCMSource.getProjectId();
+                        if (projectId != null
+                                && projectId.equals(
+                                        getPayload().getMergeRequest().getTargetProjectId())
                                 && isTrustedMember(gitLabSCMSource, sourceContext.getOnlyTrustedMembersCanTrigger())) {
                             for (Job<?, ?> job : owner.getAllJobs()) {
                                 if (MultiBranchProject.class.isAssignableFrom(
diff --git a/src/main/java/io/jenkins/plugins/gitlabbranchsource/GitLabSCMSource.java b/src/main/java/io/jenkins/plugins/gitlabbranchsource/GitLabSCMSource.java
index 295bb51e..f3019535 100644
--- a/src/main/java/io/jenkins/plugins/gitlabbranchsource/GitLabSCMSource.java
+++ b/src/main/java/io/jenkins/plugins/gitlabbranchsource/GitLabSCMSource.java
@@ -237,12 +237,12 @@ public HashMap<String, AccessLevel> getMembers() {
         return members;
     }
 
-    public long getProjectId() {
+    public Long getProjectId() {
         return projectId;
     }
 
     @DataBoundSetter
-    public void setProjectId(long projectId) {
+    public void setProjectId(Long projectId) {
         this.projectId = projectId;
     }
 
diff --git a/src/test/java/io/jenkins/plugins/gitlabbranchsource/GitLabSCMSourceDeserializationTest.java b/src/test/java/io/jenkins/plugins/gitlabbranchsource/GitLabSCMSourceDeserializationTest.java
index 2c965e4f..4326b01e 100644
--- a/src/test/java/io/jenkins/plugins/gitlabbranchsource/GitLabSCMSourceDeserializationTest.java
+++ b/src/test/java/io/jenkins/plugins/gitlabbranchsource/GitLabSCMSourceDeserializationTest.java
@@ -1,5 +1,6 @@
 package io.jenkins.plugins.gitlabbranchsource;
 
+import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
 
 import java.lang.reflect.Field;
@@ -43,4 +44,25 @@ public void afterRestartingJenkinsTransientFieldsAreNotNull() throws Exception {
             assertNotNull(mergeRequestContributorCache.get(source));
         });
     }
+
+    @Test
+    public void projectIdSurvivesConfigRoundtrip() {
+        plan.then(j -> {
+            GitLabSCMSourceBuilder sb =
+                    new GitLabSCMSourceBuilder(SOURCE_ID, "server", "creds", "po", "group/project", "project");
+            WorkflowMultiBranchProject project = j.createProject(WorkflowMultiBranchProject.class, PROJECT_NAME);
+            GitLabSCMSource source = sb.build();
+            project.getSourcesList().add(new BranchSource(source));
+            long p = 42;
+            source.setProjectId(p);
+            j.configRoundtrip(project);
+
+            WorkflowMultiBranchProject item =
+                    j.jenkins.getItemByFullName(PROJECT_NAME, WorkflowMultiBranchProject.class);
+            assertNotNull(item);
+            GitLabSCMSource scmSource = (GitLabSCMSource) item.getSCMSource(SOURCE_ID);
+            assertNotNull(scmSource);
+            assertEquals(Long.valueOf(p), scmSource.getProjectId());
+        });
+    }
 }