diff --git a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/BaseClassLookup.java b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/BaseClassLookup.java
index e7870df9770..fa81745af61 100644
--- a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/BaseClassLookup.java
+++ b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/BaseClassLookup.java
@@ -238,7 +238,7 @@ class BaseClassLookup {
 					}
 
 					ICPPClassType grandBaseClass = (ICPPClassType) grandBaseBinding;
-					if (data.contentAssist && grandBaseClass instanceof ICPPDeferredClassInstance) {
+					if (data.fHeuristicBaseLookup && grandBaseClass instanceof ICPPDeferredClassInstance) {
 						// Support content assist for members of deferred instances.
 						grandBaseClass= ((ICPPDeferredClassInstance) grandBaseClass).getClassTemplate();
 					}
diff --git a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/CPPSemantics.java b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/CPPSemantics.java
index e777ba1c0aa..3c9a481d66d 100644
--- a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/CPPSemantics.java
+++ b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/CPPSemantics.java
@@ -1151,6 +1151,7 @@ public class CPPSemantics {
 		ld2.setIgnorePointOfDeclaration(data.isIgnorePointOfDeclaration());
 		ld2.contentAssist= data.contentAssist;
 		ld2.fNoNarrowing= data.fNoNarrowing;
+		ld2.fHeuristicBaseLookup= data.fHeuristicBaseLookup;
 		ld2.qualified= parent instanceof ICPPASTQualifiedName;
 		ld2.typesOnly= true;
 		lookup(ld2, getLookupScope(typeDtorName));
@@ -3787,6 +3788,7 @@ public class CPPSemantics {
 			String[] additionalNamespaces) {
 		LookupData data = createLookupData(name);
 		data.contentAssist = true;
+		data.fHeuristicBaseLookup = true;
 		data.setPrefixLookup(prefixLookup);
 		data.foundItems = new CharArrayObjectMap<>(2);
 
diff --git a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/LookupData.java b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/LookupData.java
index 51426f5eb33..b1649124a3a 100644
--- a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/LookupData.java
+++ b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/LookupData.java
@@ -103,6 +103,9 @@ public class LookupData extends ScopeLookupData {
 	public boolean argsContainImpliedObject;
 	/** In list-initialization **/
 	public boolean fNoNarrowing;
+	/** When doing lookup in base classes, replace deferred class instances with their class template.
+	 *  This is used by editor actions like content assist. */
+	public boolean fHeuristicBaseLookup;
 
 	private IASTDeclarator fDeclarator;
 	private boolean fFunctionCall;