diff --git a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/AccessContext.java b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/AccessContext.java
index fc290600c7b..1625e78e331 100644
--- a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/AccessContext.java
+++ b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/AccessContext.java
@@ -36,6 +36,7 @@ import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPClosureType;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.ClassTypeHelper;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.ICPPDeferredClassInstance;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.ICPPInternalUnknownScope;
+import org.eclipse.cdt.internal.core.dom.parser.cpp.ICPPUnknownMemberClass;
 
 /**
  * The context that determines access to private and protected class members.
@@ -82,13 +83,19 @@ public class AccessContext {
 	 * A class through which the bindings are accessed (11.2.4).
 	 */
 	private boolean isUnqualifiedLookup;
+	private boolean isPrefixLookup;
 	private ICPPClassType namingClass;  // Depends on the binding for which we check the access.
 	// The first candidate is independent of the binding for which we do the access-check.
 	private ICPPClassType firstCandidateForNamingClass;
 	private DOMException initializationException;
 
 	public AccessContext(IASTName name) {
+		this(name, false);
+	}
+
+	public AccessContext(IASTName name, boolean prefixLookup) {
 		this.name = name;
+		this.isPrefixLookup = prefixLookup;
 	}
 
 	/**
@@ -296,6 +303,13 @@ public class AccessContext {
 				if (scopeType instanceof ICPPDeferredClassInstance) {
 					return ((ICPPDeferredClassInstance) scopeType).getClassTemplate();
 				}
+				if (scopeType instanceof ICPPUnknownMemberClass && isPrefixLookup) {
+					scopeType = HeuristicResolver.resolveUnknownType((ICPPUnknownMemberClass) scopeType,
+							name.getParent());
+					if (scopeType instanceof ICPPClassType) {
+						return (ICPPClassType) scopeType;
+					}
+				}
 			}
 
 			scope = CPPSemantics.getParentScope(scope, data.getTranslationUnit());
diff --git a/core/org.eclipse.cdt.ui.tests/ui/org/eclipse/cdt/ui/tests/text/contentassist2/CompletionTests.java b/core/org.eclipse.cdt.ui.tests/ui/org/eclipse/cdt/ui/tests/text/contentassist2/CompletionTests.java
index 267fefb98c7..5ccfc967e6b 100644
--- a/core/org.eclipse.cdt.ui.tests/ui/org/eclipse/cdt/ui/tests/text/contentassist2/CompletionTests.java
+++ b/core/org.eclipse.cdt.ui.tests/ui/org/eclipse/cdt/ui/tests/text/contentassist2/CompletionTests.java
@@ -590,6 +590,22 @@ public class CompletionTests extends CompletionTestBase {
 		assertCompletionResults(fCursorOffset, expected, ID);
 	}
 
+	// template <typename TPA>
+	// struct A {
+	//   struct AA {
+	//     static int i;
+	//   };
+	// };
+	//
+	// template <typename TPB>
+	// void test()
+	// {
+	//   A<TPB>::AA::/*cursor*/
+	// }
+	public void testUnknownMemberClassAccessContext_520783() throws Exception {
+		assertCompletionResults(new String[] { "i" });
+	}
+
 	//	template <typename T>
 	//	struct A {
 	//		template <typename U>
@@ -1126,51 +1142,7 @@ public class CompletionTests extends CompletionTestBase {
 		final String[] expected= { "add(tOther)" };
 		assertCompletionResults(fCursorOffset, expected, REPLACEMENT);
 	}
-	
-	// template <typename TPA>
-	// struct A {
-	//   struct {
-	//     int i;
-	//   } test;
-	// };
-	//
-	// template <typename TPB>
-	// struct B {
-	//
-	// A<TPB> const* a;
-	//
-	// void
-	// test()
-	// {
-	//   a->test./*cursor*/
-	// }
-	// };
-	public void testHeuristicTypeResolution1_520470() throws Exception {
-		assertCompletionResults(new String[] { "i" });
-	}
-	
-	// template <typename TPA>
-	// struct A {
-	//   struct {
-	//     int i;
-	//   } test;
-	// };
-	//
-	// template <typename TPB>
-	// struct B {
-	//
-	// A<TPB> const* a();
-	//
-	// void
-	// test()
-	// {
-	//   a()->t/*cursor*/
-	// }
-	// };
-	public void testHeuristicTypeResolution2_520470() throws Exception {
-		assertCompletionResults(new String[] { "test" });
-	}
-	
+
 	//namespace ns {
 	//  template<class T>
 	//  class Base {
diff --git a/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/contentassist/DOMCompletionProposalComputer.java b/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/contentassist/DOMCompletionProposalComputer.java
index 66657d824af..52360c7299c 100644
--- a/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/contentassist/DOMCompletionProposalComputer.java
+++ b/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/contentassist/DOMCompletionProposalComputer.java
@@ -183,7 +183,7 @@ public class DOMCompletionProposalComputer extends ParsingBasedProposalComputer
 				IBinding[] bindings = astContext.findBindings(name, !context.isContextInformationStyle());
 
 				if (bindings != null) {
-					AccessContext accessibilityContext = new AccessContext(name);
+					AccessContext accessibilityContext = new AccessContext(name, true);
 					for (IBinding binding : bindings) {
 						if (accessibilityContext.isAccessible(binding))
 							handleBinding(binding, context, prefix, astContext, proposals);
@@ -844,7 +844,7 @@ public class DOMCompletionProposalComputer extends ParsingBasedProposalComputer
 		});
 
 		Map<String, IBinding> elementsMap = new HashMap<>();
-		AccessContext accessibilityContext = new AccessContext(name);
+		AccessContext accessibilityContext = new AccessContext(name, true);
 		for (IBinding binding : bindings) {
 			// Consider only fields and variables that are declared in the current translation unit.
 			if (binding instanceof IVariable