diff --git a/src/libexpr/nix_api_expr.cc b/src/libexpr/nix_api_expr.cc
index 1eb3693a2..84d55ec13 100644
--- a/src/libexpr/nix_api_expr.cc
+++ b/src/libexpr/nix_api_expr.cc
@@ -132,9 +132,12 @@ void nix_gc_decref(const void *p) {
   // todo: else { throw? }
 }
 
+void nix_gc_now() { GC_gcollect(); }
+
 #else
-void nix_gc_incref(const void *){};
-void nix_gc_decref(const void *){};
+void nix_gc_incref(const void *) {}
+void nix_gc_decref(const void *) {}
+void nix_gc_now() {}
 #endif
 
 void nix_gc_register_finalizer(void *obj, void *cd,
diff --git a/src/libexpr/nix_api_expr.h b/src/libexpr/nix_api_expr.h
index ae2806343..9efb3dde1 100644
--- a/src/libexpr/nix_api_expr.h
+++ b/src/libexpr/nix_api_expr.h
@@ -128,6 +128,13 @@ void nix_gc_incref(const void *);
  */
 void nix_gc_decref(const void *);
 
+/**
+ * @brief Trigger the garbage collector manually
+ *
+ * You should not need to do this, but it can be useful for debugging.
+ */
+void nix_gc_now();
+
 /**
  * @brief Register a callback that gets called when the object is garbage
  * collected.