diff --git a/org.eclipse.xtext/src/org/eclipse/xtext/xtext/OverriddenValueInspector.java b/org.eclipse.xtext/src/org/eclipse/xtext/xtext/OverriddenValueInspector.java
index 25b6a7ec5..6f840ae47 100644
--- a/org.eclipse.xtext/src/org/eclipse/xtext/xtext/OverriddenValueInspector.java
+++ b/org.eclipse.xtext/src/org/eclipse/xtext/xtext/OverriddenValueInspector.java
@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2009 itemis AG (http://www.itemis.eu) and others.
+ * Copyright (c) 2009, 2020 itemis AG (http://www.itemis.eu) and others.
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Public License 2.0 which is available at
  * http://www.eclipse.org/legal/epl-2.0.
@@ -10,6 +10,8 @@ package org.eclipse.xtext.xtext;
 
 import java.util.Collection;
 import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
 import java.util.Set;
 
 import org.eclipse.xtext.AbstractElement;
@@ -25,6 +27,7 @@ import org.eclipse.xtext.RuleCall;
 import org.eclipse.xtext.TerminalRule;
 import org.eclipse.xtext.validation.ValidationMessageAcceptor;
 
+import com.google.common.collect.ImmutableMultimap;
 import com.google.common.collect.LinkedHashMultimap;
 import com.google.common.collect.Lists;
 import com.google.common.collect.Multimap;
@@ -40,16 +43,19 @@ public class OverriddenValueInspector extends XtextRuleInspector<Boolean, Parser
 	private Multimap<String, AbstractElement> assignedFeatures;
 	
 	/**
-	 * Remember all visited unassigned rule calls in case the grammar is broken, e.g. has
+	 * Remember all visited rules in case the grammar is broken, e.g. has
 	 * no assignments (yet).
 	 */
 	private Set<AbstractRule> permanentlyVisited;
 	
 	private Set<RuleCall> fragmentStack;
 	
+	private Map<AbstractRule, ImmutableMultimap<String, AbstractElement>> assignedFeaturesAtEnd;
+	
 	public OverriddenValueInspector(ValidationMessageAcceptor acceptor) {
 		super(acceptor);
 		assignedFeatures = newMultimap();
+		assignedFeaturesAtEnd = new HashMap<>();
 		permanentlyVisited = Sets.newHashSet();
 		fragmentStack = Sets.newHashSet();
 	}
@@ -73,6 +79,10 @@ public class OverriddenValueInspector extends XtextRuleInspector<Boolean, Parser
 	
 	@Override
 	protected Boolean doInspect(ParserRule rule) {
+		permanentlyVisited.clear();
+		fragmentStack.clear();
+		assignedFeatures.clear();
+		visitedRules.clear();
 		return doSwitch(rule.getAlternatives());
 	}
 	
@@ -160,9 +170,16 @@ public class OverriddenValueInspector extends XtextRuleInspector<Boolean, Parser
 		if (!addVisited(parserRule))
 			return Boolean.FALSE;
 		Multimap<String, AbstractElement> prevAssignedFeatures = assignedFeatures;
-		assignedFeatures = newMultimap();
-		doSwitch(parserRule.getAlternatives());
-		for (String feature : assignedFeatures.keySet())
+		
+		// Cannot use #computeIfAbsent since we will call this recursively and that causes ConcurrentModificationExceptions
+		ImmutableMultimap<String, AbstractElement> assignedInCalledRule = assignedFeaturesAtEnd.get(parserRule);
+		if (assignedInCalledRule == null) {
+			assignedFeatures = newMultimap();
+			doSwitch(parserRule.getAlternatives());
+			assignedInCalledRule = ImmutableMultimap.copyOf(assignedFeatures);
+			assignedFeaturesAtEnd.put(parserRule, assignedInCalledRule);
+		}
+		for (String feature : assignedInCalledRule.keySet())
 			prevAssignedFeatures.put(feature, object);
 		assignedFeatures = prevAssignedFeatures;
 		removeVisited(parserRule);
diff --git a/org.eclipse.xtext/src/org/eclipse/xtext/xtext/PredicateUsesUnorderedGroupInspector.java b/org.eclipse.xtext/src/org/eclipse/xtext/xtext/PredicateUsesUnorderedGroupInspector.java
index 033547fbd..c99605228 100644
--- a/org.eclipse.xtext/src/org/eclipse/xtext/xtext/PredicateUsesUnorderedGroupInspector.java
+++ b/org.eclipse.xtext/src/org/eclipse/xtext/xtext/PredicateUsesUnorderedGroupInspector.java
@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2011 itemis AG (http://www.itemis.eu) and others.
+ * Copyright (c) 2011, 2020 itemis AG (http://www.itemis.eu) and others.
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Public License 2.0 which is available at
  * http://www.eclipse.org/legal/epl-2.0.
@@ -63,7 +63,7 @@ public class PredicateUsesUnorderedGroupInspector extends XtextSwitch<Boolean> i
 				validatedRules = Sets.newHashSet();
 				doSwitch(rule);
 				storedRules.addAll(validatedRules);
-				storedRules = validatedRules;
+				validatedRules = storedRules;
 			}
 		}
 	}
diff --git a/org.eclipse.xtext/src/org/eclipse/xtext/xtext/XtextRuleInspector.java b/org.eclipse.xtext/src/org/eclipse/xtext/xtext/XtextRuleInspector.java
index a4ee6c779..98cf87d4d 100644
--- a/org.eclipse.xtext/src/org/eclipse/xtext/xtext/XtextRuleInspector.java
+++ b/org.eclipse.xtext/src/org/eclipse/xtext/xtext/XtextRuleInspector.java
@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2009 itemis AG (http://www.itemis.eu) and others.
+ * Copyright (c) 2009, 2020 itemis AG (http://www.itemis.eu) and others.
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Public License 2.0 which is available at
  * http://www.eclipse.org/legal/epl-2.0.
@@ -28,7 +28,7 @@ public abstract class XtextRuleInspector<Result, RuleType extends AbstractRule>
 
 	private final ValidationMessageAcceptor acceptor;
 
-	private Collection<AbstractRule> visitedRules;
+	Collection<AbstractRule> visitedRules;
 	
 	public XtextRuleInspector(ValidationMessageAcceptor acceptor) {
 		this.acceptor = acceptor;
diff --git a/org.eclipse.xtext/src/org/eclipse/xtext/xtext/XtextScopeProvider.java b/org.eclipse.xtext/src/org/eclipse/xtext/xtext/XtextScopeProvider.java
index 84d57a37b..699dd4829 100644
--- a/org.eclipse.xtext/src/org/eclipse/xtext/xtext/XtextScopeProvider.java
+++ b/org.eclipse.xtext/src/org/eclipse/xtext/xtext/XtextScopeProvider.java
@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2008 itemis AG (http://www.itemis.eu) and others.
+ * Copyright (c) 2008, 2020 itemis AG (http://www.itemis.eu) and others.
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Public License 2.0 which is available at
  * http://www.eclipse.org/legal/epl-2.0.
@@ -9,7 +9,6 @@
 package org.eclipse.xtext.xtext;
 
 import java.util.ArrayList;
-import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
 
@@ -49,6 +48,7 @@ import org.eclipse.xtext.scoping.impl.SimpleScope;
 
 import com.google.common.base.Function;
 import com.google.common.base.Predicate;
+import com.google.common.collect.FluentIterable;
 import com.google.common.collect.Iterables;
 import com.google.common.collect.Lists;
 import com.google.inject.Inject;
@@ -73,7 +73,7 @@ public class XtextScopeProvider extends AbstractScopeProvider {
 				if (metaModel != null) {
 					EPackage pack = metaModel.getEPackage();
 					if (pack != null)
-						return createClassifierScope(pack.getEClassifiers());
+						return createClassifierScope(Collections.singletonList(pack));
 				} else {
 					return createReferencedPackagesScope(GrammarUtil.getGrammar(context));
 				}
@@ -123,31 +123,50 @@ public class XtextScopeProvider extends AbstractScopeProvider {
 	}
 
 	protected IScope createEnumLiteralsScope(EEnum eEnum) {
-		return new SimpleScope(IScope.NULLSCOPE,Iterables.transform(eEnum.getELiterals(), new Function<EEnumLiteral, IEObjectDescription>() {
-							@Override
-							public IEObjectDescription apply(EEnumLiteral param) {
-								return EObjectDescription.create(QualifiedName.create(param.getName()), param);
-							}
-						}));
+		return new SimpleScope(IScope.NULLSCOPE, Iterables.transform(eEnum.getELiterals(), new Function<EEnumLiteral, IEObjectDescription>() {
+			@Override
+			public IEObjectDescription apply(EEnumLiteral param) {
+				return EObjectDescription.create(QualifiedName.create(param.getName()), param);
+			}
+		}));
 	}
 
-	protected IScope createClassifierScope(Iterable<EClassifier> classifiers) {
+	protected IScope createClassifierScope(List<EPackage> packages) {
 		return new SimpleScope(
-				IScope.NULLSCOPE,Iterables.transform(classifiers, new Function<EClassifier, IEObjectDescription>() {
-					@Override
-					public IEObjectDescription apply(EClassifier param) {
-						return EObjectDescription.create(QualifiedName.create(param.getName()), param);
+				IScope.NULLSCOPE, 
+				FluentIterable.from(packages)
+					.transformAndConcat(EPackage::getEClassifiers)
+					.transform(classifier->EObjectDescription.create(QualifiedName.create(classifier.getName()), classifier))) {
+			
+			@Override
+			protected IEObjectDescription getSingleLocalElementByName(QualifiedName name) {
+				if (name.getSegmentCount() == 1) {
+					EClassifier candidate = null;
+					for(EPackage pack: packages) {
+						EClassifier classifier = pack.getEClassifier(name.getFirstSegment());
+						if (classifier != null) {
+							if (candidate != null) {
+								return null;
+							}
+							candidate = classifier;
+						}
 					}
-				}));
+					if (candidate != null) {
+						return EObjectDescription.create(name, candidate);
+					}
+				}
+				return null;
+			}
+		};
 	}
 
 	protected IScope createReferencedPackagesScope(Grammar g) {
-		final Collection<EClassifier> allClassifiers = new ArrayList<EClassifier>();
+		List<EPackage> allPackages = new ArrayList<EPackage>();
 		for(AbstractMetamodelDeclaration decl: g.getMetamodelDeclarations()) {
 			if (decl.getEPackage() != null)
-				allClassifiers.addAll(decl.getEPackage().getEClassifiers());
+				allPackages.add(decl.getEPackage());
 		}
-		return createClassifierScope(allClassifiers);
+		return createClassifierScope(allPackages);
 	}
 
 	protected IScope createScope(Resource resource, EClass type, IScope parent) {
@@ -164,7 +183,7 @@ public class XtextScopeProvider extends AbstractScopeProvider {
 		if (EcorePackage.Literals.EPACKAGE == type) {
 			return createEPackageScope(grammar);
 		} else if (AbstractMetamodelDeclaration.class.isAssignableFrom(type.getInstanceClass())) {
-			return new SimpleScope(IScope.NULLSCOPE,Iterables.transform(grammar.getMetamodelDeclarations(),
+			return new SimpleScope(IScope.NULLSCOPE, Iterables.transform(grammar.getMetamodelDeclarations(),
 							new Function<AbstractMetamodelDeclaration,IEObjectDescription>(){
 								@Override
 								public IEObjectDescription apply(AbstractMetamodelDeclaration from) {
diff --git a/org.eclipse.xtext/src/org/eclipse/xtext/xtext/XtextValidator.java b/org.eclipse.xtext/src/org/eclipse/xtext/xtext/XtextValidator.java
index e258beaca..61e26dc1a 100644
--- a/org.eclipse.xtext/src/org/eclipse/xtext/xtext/XtextValidator.java
+++ b/org.eclipse.xtext/src/org/eclipse/xtext/xtext/XtextValidator.java
@@ -1062,9 +1062,13 @@ public class XtextValidator extends AbstractDeclarativeValidator {
 	}
 
 	@Check
-	public void checkForOverriddenValue(final ParserRule rule) {
+	public void checkForOverriddenValue(final Grammar grammar) {
 		OverriddenValueInspector inspector = new OverriddenValueInspector(this);
-		inspector.inspect(rule);
+		for(AbstractRule rule: grammar.getRules()) {
+			if (rule instanceof ParserRule) {
+				inspector.inspect((ParserRule) rule);
+			}
+		}
 	}
 	
 	@Check