diff --git a/kdevplatform/language/duchain/navigation/abstractdeclarationnavigationcontext.h b/kdevplatform/language/duchain/navigation/abstractdeclarationnavigationcontext.h
--- a/kdevplatform/language/duchain/navigation/abstractdeclarationnavigationcontext.h
+++ b/kdevplatform/language/duchain/navigation/abstractdeclarationnavigationcontext.h
@@ -68,7 +68,7 @@
     static QString stringFromAccess(const DeclarationPointer& decl);
     QString declarationName(const DeclarationPointer& decl) const;
     static QStringList declarationDetails(const DeclarationPointer& decl);
-    static QString declarationSizeInformation(const DeclarationPointer& decl);
+    static QString declarationSizeInformation(const DeclarationPointer& decl, const TopDUContext* topContext);
 
     ///This can be used for example to resolve typedefs within the type.
     ///All types that are visualized in the navigation-context are/should be mangled through this.
diff --git a/kdevplatform/language/duchain/navigation/abstractdeclarationnavigationcontext.cpp b/kdevplatform/language/duchain/navigation/abstractdeclarationnavigationcontext.cpp
--- a/kdevplatform/language/duchain/navigation/abstractdeclarationnavigationcontext.cpp
+++ b/kdevplatform/language/duchain/navigation/abstractdeclarationnavigationcontext.cpp
@@ -353,7 +353,7 @@
     }
 
     if (!shorten) {
-        modifyHtml() += declarationSizeInformation(d->m_declaration);
+        modifyHtml() += declarationSizeInformation(d->m_declaration, topContext().data());
     }
 
     if (!shorten && doc) {
@@ -841,8 +841,21 @@
     return details;
 }
 
-QString AbstractDeclarationNavigationContext::declarationSizeInformation(const DeclarationPointer& decl)
+QString AbstractDeclarationNavigationContext::declarationSizeInformation(const DeclarationPointer& decl,
+                                                                         const TopDUContext* topContext)
 {
+    if (!decl) {
+        return {};
+    }
+
+    if (decl->isTypeAlias()) {
+        // show size information for underlying type of aliases / typedefs etc.
+        const auto type = TypeUtils::targetType(decl->abstractType(), topContext);
+        if (const auto* idType = dynamic_cast<const IdentifiedType*>(type.data())) {
+            return declarationSizeInformation(DeclarationPointer(idType->declaration(topContext)), topContext);
+        }
+        return {};
+    }
     // Note that ClassMemberDeclaration also includes ClassDeclaration, which uses the sizeOf and alignOf fields,
     // but normally leaves the bitOffsetOf unset (-1).
     const auto* memberDecl = dynamic_cast<const ClassMemberDeclaration*>(decl.data());