diff --git a/src/libexpr/eval-gc.hh b/src/libexpr/eval-gc.hh
index 8f492c56d8c..1be9ff65b57 100644
--- a/src/libexpr/eval-gc.hh
+++ b/src/libexpr/eval-gc.hh
@@ -22,9 +22,10 @@ using traceable_allocator = std::allocator<T>;
 template<typename T>
 using gc_allocator = std::allocator<T>;
 
-#define GC_MALLOC_ATOMIC std::malloc
-#define GC_STRDUP std::strdup
-struct gc { };
+#  define GC_MALLOC_ATOMIC std::malloc
+#  define GC_STRDUP std::strdup
+struct gc
+{};
 
 #endif