diff --git a/src/libutil/nar-accessor.cc b/src/libutil/nar-accessor.cc
index e43d43aac0b..040c7d0c892 100644
--- a/src/libutil/nar-accessor.cc
+++ b/src/libutil/nar-accessor.cc
@@ -4,6 +4,7 @@
 
 #include <map>
 #include <stack>
+#include <utility>
 
 #include <nlohmann/json.hpp>
 
@@ -332,6 +333,8 @@ static ListNarResult<deep> listNarImpl(SourceAccessor & accessor, const CanonPat
     case SourceAccessor::Type::tUnknown:
         assert(false); // cannot happen for NARs
     }
+
+    unreachable();
 }
 
 NarListing listNarDeep(SourceAccessor & accessor, const CanonPath & path)