diff --git a/Userland/DevTools/HackStudio/LanguageServers/Cpp/ParserAutoComplete.cpp b/Userland/DevTools/HackStudio/LanguageServers/Cpp/ParserAutoComplete.cpp
index 2a8b598092..e3c195a4db 100644
--- a/Userland/DevTools/HackStudio/LanguageServers/Cpp/ParserAutoComplete.cpp
+++ b/Userland/DevTools/HackStudio/LanguageServers/Cpp/ParserAutoComplete.cpp
@@ -44,12 +44,7 @@ OwnPtr<ParserAutoComplete::DocumentData> ParserAutoComplete::create_document_dat
     auto document = filedb().get_or_create_from_filesystem(file);
     if (!document)
         return {};
-    auto content = document->text();
-    auto document_data = create_document_data(document->text(), file);
-
-    update_declared_symbols(*document_data);
-
-    return document_data;
+    return create_document_data(document->text(), file);
 }
 
 void ParserAutoComplete::set_document_data(const String& file, OwnPtr<DocumentData>&& data)
@@ -260,13 +255,8 @@ Vector<ParserAutoComplete::PropertyInfo> ParserAutoComplete::properties_of_type(
 NonnullRefPtrVector<Declaration> ParserAutoComplete::get_global_declarations_including_headers(const DocumentData& document) const
 {
     NonnullRefPtrVector<Declaration> declarations;
-    for (auto& include : document.preprocessor().included_paths()) {
-        document_path_from_include_path(include);
-        auto included_document = get_document_data(document_path_from_include_path(include));
-        if (!included_document)
-            continue;
-        declarations.append(get_global_declarations_including_headers(*included_document));
-    }
+    for (auto& decl : document.m_declarations_from_headers)
+        declarations.append(*decl);
 
     declarations.append(get_global_declarations(*document.parser().root_node()));
 
@@ -434,8 +424,16 @@ RefPtr<Declaration> ParserAutoComplete::find_declaration_of(const DocumentData&
     return {};
 }
 
-void ParserAutoComplete::update_declared_symbols(const DocumentData& document)
+void ParserAutoComplete::update_declared_symbols(DocumentData& document)
 {
+    for (auto& include : document.preprocessor().included_paths()) {
+        auto included_document = get_or_create_document_data(document_path_from_include_path(include));
+        if (!included_document)
+            continue;
+        for (auto&& decl : get_global_declarations_including_headers(*included_document))
+            document.m_declarations_from_headers.set(move(decl));
+    }
+
     Vector<GUI::AutocompleteProvider::Declaration> declarations;
 
     for (auto& decl : get_global_declarations(*document.parser().root_node())) {
@@ -494,6 +492,8 @@ OwnPtr<ParserAutoComplete::DocumentData> ParserAutoComplete::create_document_dat
     if constexpr (CPP_LANGUAGE_SERVER_DEBUG)
         root->dump(0);
 
+    update_declared_symbols(*document_data);
+
     return document_data;
 }
 
diff --git a/Userland/DevTools/HackStudio/LanguageServers/Cpp/ParserAutoComplete.h b/Userland/DevTools/HackStudio/LanguageServers/Cpp/ParserAutoComplete.h
index 5d8c4487db..39db9c8656 100644
--- a/Userland/DevTools/HackStudio/LanguageServers/Cpp/ParserAutoComplete.h
+++ b/Userland/DevTools/HackStudio/LanguageServers/Cpp/ParserAutoComplete.h
@@ -59,6 +59,9 @@ private:
         String m_text;
         OwnPtr<Preprocessor> m_preprocessor;
         OwnPtr<Parser> m_parser;
+
+        // FIXME: This HashTable must be re-computed if a declaration from a header file is modified
+        HashTable<NonnullRefPtr<Declaration>> m_declarations_from_headers;
     };
 
     Vector<GUI::AutocompleteProvider::Entry> autocomplete_property(const DocumentData&, const MemberExpression&, const String partial_text) const;
@@ -85,7 +88,7 @@ private:
 
     OwnPtr<DocumentData> create_document_data_for(const String& file);
     String document_path_from_include_path(const StringView& include_path) const;
-    void update_declared_symbols(const DocumentData&);
+    void update_declared_symbols(DocumentData&);
     GUI::AutocompleteProvider::DeclarationType type_of_declaration(const Declaration&);
     String scope_of_declaration(const Declaration&);
     Optional<GUI::AutocompleteProvider::ProjectLocation> find_preprocessor_definition(const DocumentData&, const GUI::TextPosition&);