diff --git a/build/org.eclipse.cdt.make.core/src/org/eclipse/cdt/make/internal/core/MakeTarget.java b/build/org.eclipse.cdt.make.core/src/org/eclipse/cdt/make/internal/core/MakeTarget.java
index 1616ebf75c3..d1c4db44c26 100644
--- a/build/org.eclipse.cdt.make.core/src/org/eclipse/cdt/make/internal/core/MakeTarget.java
+++ b/build/org.eclipse.cdt.make.core/src/org/eclipse/cdt/make/internal/core/MakeTarget.java
@@ -333,7 +333,7 @@ public class MakeTarget extends PlatformObject implements IMakeTarget {
 			}
 		};
 		try {
-			ResourcesPlugin.getWorkspace().run(op, monitor);
+			ResourcesPlugin.getWorkspace().run(op, null, IResource.NONE, monitor);
 		} finally {
 			monitor.done();
 		}
diff --git a/build/org.eclipse.cdt.make.ui/src/org/eclipse/cdt/make/ui/TargetBuild.java b/build/org.eclipse.cdt.make.ui/src/org/eclipse/cdt/make/ui/TargetBuild.java
index 0a804d4a074..e53aa256d64 100644
--- a/build/org.eclipse.cdt.make.ui/src/org/eclipse/cdt/make/ui/TargetBuild.java
+++ b/build/org.eclipse.cdt.make.ui/src/org/eclipse/cdt/make/ui/TargetBuild.java
@@ -18,6 +18,7 @@ import org.eclipse.cdt.make.core.IMakeTarget;
 import org.eclipse.cdt.make.internal.ui.MakeUIPlugin;
 import org.eclipse.cdt.make.internal.ui.preferences.MakePreferencePage;
 import org.eclipse.core.resources.IFile;
+import org.eclipse.core.resources.IResource;
 import org.eclipse.core.resources.IWorkspaceRunnable;
 import org.eclipse.core.resources.ResourcesPlugin;
 import org.eclipse.core.runtime.CoreException;
@@ -100,7 +101,7 @@ public class TargetBuild {
 								target.build(new SubProgressMonitor(monitor, 1));
 							}
 						};
-						MakeUIPlugin.getWorkspace().run(runnable, monitor);
+						MakeUIPlugin.getWorkspace().run(runnable, null, IResource.NONE, monitor);
 					}
 				} catch (CoreException e) {
 					return e.getStatus();
diff --git a/build/org.eclipse.cdt.managedbuilder.core/src/org/eclipse/cdt/managedbuilder/internal/core/CommonBuilder.java b/build/org.eclipse.cdt.managedbuilder.core/src/org/eclipse/cdt/managedbuilder/internal/core/CommonBuilder.java
index 5fc270eabc0..2e7f41806d1 100644
--- a/build/org.eclipse.cdt.managedbuilder.core/src/org/eclipse/cdt/managedbuilder/internal/core/CommonBuilder.java
+++ b/build/org.eclipse.cdt.managedbuilder.core/src/org/eclipse/cdt/managedbuilder/internal/core/CommonBuilder.java
@@ -22,8 +22,8 @@ import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
-import java.util.Set;
 import java.util.Map.Entry;
+import java.util.Set;
 
 import org.eclipse.cdt.build.core.scannerconfig.CfgInfoContext;
 import org.eclipse.cdt.build.core.scannerconfig.ICfgScannerConfigBuilderInfo2Set;
@@ -2078,4 +2078,30 @@ public class CommonBuilder extends ACBuilder {
 		if (markers != null) {
 			workspace.deleteMarkers(markers);
 		}
-	}}
+	}
+
+	/**
+	 * Only lock the workspace is this is a ManagedBuild, or this project references others.
+	 */
+	@SuppressWarnings({ "rawtypes", "unchecked" })
+	@Override
+	public ISchedulingRule getRule(int trigger, Map args) {
+		IResource WR_rule = ResourcesPlugin.getWorkspace().getRoot();
+		if (needAllConfigBuild() || !isCdtProjectCreated(getProject()))
+			return WR_rule;
+
+		// Get the builders to run
+		IBuilder builders[] = ManagedBuilderCorePlugin.createBuilders(getProject(), args);
+		// Be pessimistic if we referenced other configs
+		if (getReferencedConfigs(builders).length > 0)
+			return WR_rule;
+		// If any builder isManaged => pessimistic
+		for (IBuilder builder : builders) {
+			if (builder.isManagedBuildOn())
+				return WR_rule;
+		}
+
+		// Success!
+		return null;
+	}
+}
diff --git a/core/org.eclipse.cdt.core/src/org/eclipse/cdt/core/resources/ACBuilder.java b/core/org.eclipse.cdt.core/src/org/eclipse/cdt/core/resources/ACBuilder.java
index 364aa68f157..d58b1950592 100644
--- a/core/org.eclipse.cdt.core/src/org/eclipse/cdt/core/resources/ACBuilder.java
+++ b/core/org.eclipse.cdt.core/src/org/eclipse/cdt/core/resources/ACBuilder.java
@@ -30,6 +30,7 @@ import org.eclipse.core.resources.IncrementalProjectBuilder;
 import org.eclipse.core.runtime.CoreException;
 import org.eclipse.core.runtime.IProgressMonitor;
 import org.eclipse.core.runtime.Preferences;
+import org.eclipse.core.runtime.jobs.ISchedulingRule;
 import org.eclipse.osgi.util.NLS;
 
 public abstract class ACBuilder extends IncrementalProjectBuilder implements IMarkerGenerator {
@@ -222,4 +223,16 @@ public abstract class ACBuilder extends IncrementalProjectBuilder implements IMa
 			printEvent(IncrementalProjectBuilder.CLEAN_BUILD, null);
 	}
 
+   /**
+	* Default ACBuilder shouldn't require locking the workspace during a CDT Project build.
+	*
+	* Note this may have a detrimental effect on #getDelta().  Derived builders which rely
+	* on #getDelta(...) being accurate should return a WorkspaceRoot scheduling rule.
+	* @since 5.2
+	*/
+	@SuppressWarnings("rawtypes")
+	public ISchedulingRule getRule(int trigger, Map args) {
+		return null;
+	}
+
 }