diff --git a/server/sonar-ce-task-projectanalysis/src/main/java/org/sonar/ce/task/projectanalysis/step/ValidateProjectStep.java b/server/sonar-ce-task-projectanalysis/src/main/java/org/sonar/ce/task/projectanalysis/step/ValidateProjectStep.java
index 098e93732d74..31f4a9869852 100644
--- a/server/sonar-ce-task-projectanalysis/src/main/java/org/sonar/ce/task/projectanalysis/step/ValidateProjectStep.java
+++ b/server/sonar-ce-task-projectanalysis/src/main/java/org/sonar/ce/task/projectanalysis/step/ValidateProjectStep.java
@@ -37,10 +37,13 @@
 import org.sonar.ce.task.step.ComputationStep;
 import org.sonar.db.DbClient;
 import org.sonar.db.DbSession;
+import org.sonar.db.component.BranchDto;
+import org.sonar.db.component.BranchType;
 import org.sonar.db.component.ComponentDao;
 import org.sonar.db.component.ComponentDto;
 import org.sonar.db.component.SnapshotDto;
 
+import static com.google.common.base.Preconditions.checkState;
 import static java.lang.String.format;
 import static org.sonar.api.utils.DateUtils.formatDateTime;
 
@@ -91,7 +94,11 @@ private void validateTargetBranch(DbSession session) {
     String mergeBranchUuid = analysisMetadataHolder.getBranch().getMergeBranchUuid().get();
     int moduleCount = dbClient.componentDao().countEnabledModulesByProjectUuid(session, mergeBranchUuid);
     if (moduleCount > 0) {
-      throw MessageException.of("Due to an upgrade, you need to re-analyze the target branch before analyzing this branch.");
+      Optional<BranchDto> opt = dbClient.branchDao().selectByUuid(session, mergeBranchUuid);
+      checkState(opt.isPresent(), "Merge branch '%s' does not exist", mergeBranchUuid);
+      String type = analysisMetadataHolder.getBranch().getType() == BranchType.PULL_REQUEST ? "pull request" : "short-lived branch";
+      throw MessageException.of(String.format(
+        "Due to an upgrade, you need first to re-analyze the target branch '%s' before analyzing this %s.", opt.get().getKey(), type));
     }
   }
 
diff --git a/server/sonar-ce-task-projectanalysis/src/test/java/org/sonar/ce/task/projectanalysis/step/ValidateProjectStepTest.java b/server/sonar-ce-task-projectanalysis/src/test/java/org/sonar/ce/task/projectanalysis/step/ValidateProjectStepTest.java
index acf221596ca3..ccfc54e67087 100644
--- a/server/sonar-ce-task-projectanalysis/src/test/java/org/sonar/ce/task/projectanalysis/step/ValidateProjectStepTest.java
+++ b/server/sonar-ce-task-projectanalysis/src/test/java/org/sonar/ce/task/projectanalysis/step/ValidateProjectStepTest.java
@@ -70,44 +70,66 @@ public class ValidateProjectStepTest {
   ValidateProjectStep underTest = new ValidateProjectStep(dbClient, treeRootHolder, analysisMetadataHolder);
 
   @Test
-  public void fail_if_pr_is_targeting_branch_with_modules() {
-    ComponentDto masterProject = ComponentTesting.newPrivateProjectDto(dbTester.organizations().insert(), "ABCD")
-      .setDbKey(PROJECT_KEY);
-    ComponentDto branchProject = ComponentTesting.newPrivateProjectDto(dbTester.organizations().insert(), "DEFG")
-      .setDbKey(PROJECT_KEY + ":BRANCH:branch");
-    dbClient.componentDao().insert(dbTester.getSession(), masterProject);
-    dbClient.componentDao().insert(dbTester.getSession(), branchProject);
+  public void fail_if_slb_is_targeting_master_with_modules() {
+    ComponentDto masterProject = dbTester.components().insertMainBranch();
     dbClient.componentDao().insert(dbTester.getSession(), ComponentTesting.newModuleDto(masterProject));
     setBranch(BranchType.SHORT, masterProject.uuid());
     dbTester.getSession().commit();
 
     treeRootHolder.setRoot(ReportComponent.builder(Component.Type.PROJECT, 1).setUuid("DEFG")
-      .setKey(branchProject.getDbKey())
+      .setKey("branch")
+      .build());
+
+    thrown.expect(MessageException.class);
+    thrown.expectMessage("Due to an upgrade, you need first to re-analyze the target branch 'master' before analyzing this short-lived branch.");
+    underTest.execute(new TestComputationStepContext());
+  }
+
+  @Test
+  public void fail_if_pr_is_targeting_branch_with_modules() {
+    ComponentDto masterProject = dbTester.components().insertMainBranch();
+    ComponentDto mergeBranch = dbTester.components().insertProjectBranch(masterProject, b -> b.setKey("mergeBranch"));
+    dbClient.componentDao().insert(dbTester.getSession(), ComponentTesting.newModuleDto(mergeBranch));
+    setBranch(BranchType.PULL_REQUEST, mergeBranch.uuid());
+    dbTester.getSession().commit();
+
+    treeRootHolder.setRoot(ReportComponent.builder(Component.Type.PROJECT, 1).setUuid("DEFG")
+      .setKey("branch")
       .build());
 
     thrown.expect(MessageException.class);
-    thrown.expectMessage("Due to an upgrade, you need to re-analyze the target branch before analyzing this branch.");
+    thrown.expectMessage("Due to an upgrade, you need first to re-analyze the target branch 'mergeBranch' before analyzing this pull request.");
     underTest.execute(new TestComputationStepContext());
   }
 
   @Test
-  public void dont_fail_if_pr_is_targeting_branch_without_modules() {
-    ComponentDto masterProject = ComponentTesting.newPrivateProjectDto(dbTester.organizations().insert(), "ABCD")
-      .setDbKey(PROJECT_KEY);
-    ComponentDto branchProject = ComponentTesting.newPrivateProjectDto(dbTester.organizations().insert(), "DEFG")
-      .setDbKey(PROJECT_KEY + ":BRANCH:branch");
-    dbClient.componentDao().insert(dbTester.getSession(), masterProject);
-    dbClient.componentDao().insert(dbTester.getSession(), branchProject);
+  public void dont_fail_if_slb_is_targeting_branch_without_modules() {
+    ComponentDto masterProject = dbTester.components().insertMainBranch();
     setBranch(BranchType.SHORT, masterProject.uuid());
     dbTester.getSession().commit();
 
     treeRootHolder.setRoot(ReportComponent.builder(Component.Type.PROJECT, 1).setUuid("DEFG")
-      .setKey(branchProject.getDbKey())
+      .setKey("branch")
       .build());
 
     underTest.execute(new TestComputationStepContext());
   }
 
+  @Test
+  public void dont_fail_for_long_forked_from_master_with_modules() {
+    ComponentDto masterProject = dbTester.components().insertMainBranch();
+    dbClient.componentDao().insert(dbTester.getSession(), ComponentTesting.newModuleDto(masterProject));
+    setBranch(BranchType.LONG, masterProject.uuid());
+    dbTester.getSession().commit();
+
+    treeRootHolder.setRoot(ReportComponent.builder(Component.Type.PROJECT, 1).setUuid("DEFG")
+      .setKey("branch")
+      .build());
+
+    underTest.execute(new TestComputationStepContext());
+  }
+
+
   private void setBranch(BranchType type, @Nullable String mergeBranchUuid) {
     Branch branch = mock(Branch.class);
     when(branch.getType()).thenReturn(type);