diff --git a/src/client_manager.cc b/src/client_manager.cc
index 540d18c7..d06e7259 100644
--- a/src/client_manager.cc
+++ b/src/client_manager.cc
@@ -175,7 +175,10 @@ void ClientManager::redraw_clients() const
 CandidateList ClientManager::complete_client_name(StringView prefix,
                                                   ByteCount cursor_pos) const
 {
-    auto c = transformed(m_clients, [](const std::unique_ptr<Client>& c){ return c->context().name(); });
+    auto c = transformed(m_clients,
+                         [](const std::unique_ptr<Client>& c) -> const String&
+                         { return c->context().name(); });
+
     return complete(prefix, cursor_pos, c);
 }
 
diff --git a/src/commands.cc b/src/commands.cc
index 0a34cd65..6304378d 100644
--- a/src/commands.cc
+++ b/src/commands.cc
@@ -60,7 +60,10 @@ const PerArgumentCommandCompleter filename_completer({
 
 static CandidateList complete_buffer_name(StringView prefix, ByteCount cursor_pos)
 {
-    auto c = transformed(BufferManager::instance(), [](const SafePtr<Buffer>& b){ return b->display_name(); });
+    auto c = transformed(BufferManager::instance(),
+                         [](const SafePtr<Buffer>& b) -> const String&
+                         { return b->display_name(); });
+
     return complete(prefix, cursor_pos, c);
 }
 
diff --git a/src/completion.hh b/src/completion.hh
index 47b08c73..1cc219c0 100644
--- a/src/completion.hh
+++ b/src/completion.hh
@@ -59,6 +59,10 @@ template<typename Container>
 CandidateList complete(StringView prefix, ByteCount cursor_pos,
                        const Container& container)
 {
+    using std::begin;
+    static_assert(not std::is_same<decltype(*begin(container)), String>::value,
+                  "complete require long lived strings");
+
     prefix = prefix.substr(0, cursor_pos);
     Vector<RankedMatch> matches;
     for (const auto& str : container)
diff --git a/src/face_registry.cc b/src/face_registry.cc
index cf404e63..53e93f78 100644
--- a/src/face_registry.cc
+++ b/src/face_registry.cc
@@ -97,7 +97,8 @@ CandidateList FaceRegistry::complete_alias_name(StringView prefix,
     using ValueType = std::pair<String, FaceOrAlias>;
     return complete(prefix, cursor_pos,
                     transformed(m_aliases,
-                                [](const ValueType& v){ return v.first; }));
+                                [](const ValueType& v) -> const String&
+                                { return v.first; }));
 }
 
 FaceRegistry::FaceRegistry()