diff --git a/src/libstore/nix_api_store.cc b/src/libstore/nix_api_store.cc
index 312e5f2a8..c81ad49ee 100644
--- a/src/libstore/nix_api_store.cc
+++ b/src/libstore/nix_api_store.cc
@@ -93,7 +93,9 @@ StorePath *nix_store_parse_path(nix_c_context *context, Store *store,
 }
 
 nix_err nix_store_build(nix_c_context *context, Store *store, StorePath *path,
-                        void (*iter)(const char *, const char *)) {
+                        void *userdata,
+                        void (*iter)(void *userdata, const char *,
+                                     const char *)) {
   if (context)
     context->last_err_code = NIX_OK;
   try {
@@ -107,7 +109,7 @@ nix_err nix_store_build(nix_c_context *context, Store *store, StorePath *path,
       for (auto &[outputName, outputPath] :
            store->ptr->queryDerivationOutputMap(path->path)) {
         auto op = store->ptr->printStorePath(outputPath);
-        iter(outputName.c_str(), op.c_str());
+        iter(userdata, outputName.c_str(), op.c_str());
       }
     }
   }
diff --git a/src/libstore/nix_api_store.h b/src/libstore/nix_api_store.h
index ba7b9ec5e..6157faa82 100644
--- a/src/libstore/nix_api_store.h
+++ b/src/libstore/nix_api_store.h
@@ -98,10 +98,13 @@ bool nix_store_is_valid_path(nix_c_context *context, Store *store,
  * @param[out] context Optional, stores error information
  * @param[in] store nix store reference
  * @param[in] path Path to build
+ * @param[in] userdata data to pass to every callback invocation
  * @param[in] cb called for every built output
  */
 nix_err nix_store_build(nix_c_context *context, Store *store, StorePath *path,
-                        void (*cb)(const char *outname, const char *out));
+                        void *userdata,
+                        void (*cb)(void *userdata, const char *outname,
+                                   const char *out));
 
 /**
  * @brief get the version of a nix store