diff --git a/ui/org.eclipse.pde.core/src/org/eclipse/pde/internal/core/PluginModelManager.java b/ui/org.eclipse.pde.core/src/org/eclipse/pde/internal/core/PluginModelManager.java
index 4511a39cd2..f983fa0e64 100644
--- a/ui/org.eclipse.pde.core/src/org/eclipse/pde/internal/core/PluginModelManager.java
+++ b/ui/org.eclipse.pde.core/src/org/eclipse/pde/internal/core/PluginModelManager.java
@@ -37,6 +37,7 @@
 import org.eclipse.core.resources.ResourcesPlugin;
 import org.eclipse.core.runtime.Adapters;
 import org.eclipse.core.runtime.CoreException;
+import org.eclipse.core.runtime.ILog;
 import org.eclipse.core.runtime.IProgressMonitor;
 import org.eclipse.core.runtime.IStatus;
 import org.eclipse.core.runtime.MultiStatus;
@@ -384,7 +385,7 @@ private void updateAffectedEntries(StateDelta delta, boolean runAsynch) {
 				index++;
 			}
 			// TODO Consider always running in a job - better reporting and cancellation options
-			if (runAsynch) {
+			if (runAsynch || ResourcesPlugin.getWorkspace().isTreeLocked()) {
 				// We may be in the UI thread, so the classpath is updated in a job to avoid blocking (bug 376135)
 				fUpdateJob.add(projects, containers);
 				fUpdateJob.schedule();
@@ -393,6 +394,7 @@ private void updateAffectedEntries(StateDelta delta, boolean runAsynch) {
 				try {
 					JavaCore.setClasspathContainer(PDECore.REQUIRED_PLUGINS_CONTAINER_PATH, projects, containers, null);
 				} catch (JavaModelException e) {
+					ILog.get().error("Setting classpath containers failed!", e); //$NON-NLS-1$
 				}
 			}
 		}
diff --git a/ui/org.eclipse.pde.ui.templates.tests/src/org/eclipse/pde/ui/templates/tests/TestPDETemplates.java b/ui/org.eclipse.pde.ui.templates.tests/src/org/eclipse/pde/ui/templates/tests/TestPDETemplates.java
index c97f22cfd2..9898d2105c 100644
--- a/ui/org.eclipse.pde.ui.templates.tests/src/org/eclipse/pde/ui/templates/tests/TestPDETemplates.java
+++ b/ui/org.eclipse.pde.ui.templates.tests/src/org/eclipse/pde/ui/templates/tests/TestPDETemplates.java
@@ -21,6 +21,7 @@
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Set;
+import java.util.concurrent.TimeUnit;
 import java.util.stream.Collectors;
 
 import org.eclipse.core.resources.IFile;
@@ -50,6 +51,7 @@
 import org.eclipse.pde.ui.IFieldData;
 import org.eclipse.pde.ui.IPluginContentWizard;
 import org.eclipse.pde.ui.tests.util.TargetPlatformUtil;
+import org.eclipse.swt.widgets.Display;
 import org.eclipse.ui.PlatformUI;
 import org.junit.Assert;
 import org.junit.Assume;
@@ -159,7 +161,26 @@ public IPath getLocationPath() {
 	@Test
 	public void configureProjectAndCheckMarkers() throws CoreException {
 		project.build(IncrementalProjectBuilder.FULL_BUILD, new NullProgressMonitor());
+		long deadline = System.currentTimeMillis() + TimeUnit.SECONDS.toMillis(60);
+		Display current = Display.getCurrent();
+		while (true) {
+			if (current != null) {
+				while (current.readAndDispatch()) {
+					Thread.onSpinWait();
+				}
+			}
+			try {
+				assertErrorFree();
+				break;
+			} catch (AssertionError e) {
+				if (System.currentTimeMillis() > deadline) {
+					throw e;
+				}
+			}
+		}
+	}
 
+	private void assertErrorFree() throws CoreException {
 		IMarker[] markers = project.findMarkers(IMarker.PROBLEM, true, IResource.DEPTH_INFINITE);
 
 		// ignore missing package export marker
@@ -179,7 +200,9 @@ public void configureProjectAndCheckMarkers() throws CoreException {
 			markers = new IMarker[0];
 		}
 
-		assertEquals("Template '" + template.getLabel() + "' generates errors.", 0, markers.length);
+		assertEquals("Template '" + template.getLabel() + "' generates errors: "
+				+ Arrays.stream(markers).map(String::valueOf).collect(Collectors.joining(System.lineSeparator())), 0,
+				markers.length);
 	}
 
 	@Test
diff --git a/ui/org.eclipse.pde.ui.tests/src/org/eclipse/pde/ui/tests/classpathcontributor/ClasspathContributorTest.java b/ui/org.eclipse.pde.ui.tests/src/org/eclipse/pde/ui/tests/classpathcontributor/ClasspathContributorTest.java
index 6a69db850b..3d3f56d3ed 100644
--- a/ui/org.eclipse.pde.ui.tests/src/org/eclipse/pde/ui/tests/classpathcontributor/ClasspathContributorTest.java
+++ b/ui/org.eclipse.pde.ui.tests/src/org/eclipse/pde/ui/tests/classpathcontributor/ClasspathContributorTest.java
@@ -18,8 +18,9 @@
 import static org.junit.Assert.assertTrue;
 
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.List;
+import java.util.concurrent.TimeUnit;
+import java.util.stream.Collectors;
 
 import org.eclipse.core.resources.IProject;
 import org.eclipse.jdt.core.IClasspathContainer;
@@ -30,6 +31,7 @@
 import org.eclipse.pde.internal.core.PDECore;
 import org.eclipse.pde.ui.tests.classpathresolver.ClasspathResolverTest;
 import org.eclipse.pde.ui.tests.util.ProjectUtils;
+import org.eclipse.swt.widgets.Display;
 import org.junit.ClassRule;
 import org.junit.Rule;
 import org.junit.Test;
@@ -50,18 +52,37 @@ public class ClasspathContributorTest {
 	@Test
 	public void testAdditionalClasspathEntries() throws Exception {
 		IProject project = ProjectUtils.importTestProject("tests/projects/" + ClasspathResolverTest.bundleName);
-		List<IClasspathEntry> expected = new ArrayList<>(TestClasspathContributor.entries);
-		expected.addAll(TestClasspathContributor.entries2);
-		IJavaProject jProject = JavaCore.create(project);
-		IClasspathContainer container = JavaCore.getClasspathContainer(PDECore.REQUIRED_PLUGINS_CONTAINER_PATH, jProject);
-		assertNotNull("Could not find PDE classpath container", container);
-		IClasspathEntry[] classpath = container.getClasspathEntries();
-		for (IClasspathEntry element : classpath) {
-			if (!isPdeDependency(element)) {
-				assertTrue("Unexpected classpath entry found: " + element, expected.remove(element));
+		long deadline = System.currentTimeMillis() + TimeUnit.SECONDS.toMillis(60);
+		while (true) {
+			Display current = Display.getCurrent();
+			if (current != null) {
+				while (current.readAndDispatch()) {
+					Thread.onSpinWait();
+				}
+			}
+			try {
+				List<IClasspathEntry> expected = new ArrayList<>(TestClasspathContributor.entries);
+				expected.addAll(TestClasspathContributor.entries2);
+				IJavaProject jProject = JavaCore.create(project);
+				IClasspathContainer container = JavaCore.getClasspathContainer(PDECore.REQUIRED_PLUGINS_CONTAINER_PATH,
+						jProject);
+				assertNotNull("Could not find PDE classpath container", container);
+				IClasspathEntry[] classpath = container.getClasspathEntries();
+				for (IClasspathEntry element : classpath) {
+					if (!isPdeDependency(element)) {
+						assertTrue("Unexpected classpath entry found: " + element, expected.remove(element));
+					}
+				}
+				assertTrue("Expected classpath entry not found: "
+						+ expected.stream().map(String::valueOf).collect(Collectors.joining(System.lineSeparator())),
+						expected.isEmpty());
+				break;
+			} catch (AssertionError e) {
+				if (System.currentTimeMillis() > deadline) {
+					throw e;
+				}
 			}
 		}
-		assertTrue("Expected classpath entry not found: " + Arrays.toString(expected.toArray()), expected.isEmpty());
 	}
 
 	private boolean isPdeDependency(IClasspathEntry element) {