diff --git a/src/libutil-test-support/include/nix/util/tests/nix_api_util.hh b/src/libutil-test-support/include/nix/util/tests/nix_api_util.hh
index 006dc497c..382c7b292 100644
--- a/src/libutil-test-support/include/nix/util/tests/nix_api_util.hh
+++ b/src/libutil-test-support/include/nix/util/tests/nix_api_util.hh
@@ -3,6 +3,7 @@
 #include "nix_api_util.h"
 
 #include <gtest/gtest.h>
+#include <string_view>
 
 namespace nixC {
 
@@ -24,7 +25,12 @@ protected:
 
     nix_c_context * ctx;
 
-    inline void assert_ctx_ok()
+    inline std::string loc(const char * file, int line)
+    {
+        return std::string(file) + ":" + std::to_string(line);
+    }
+
+    inline void assert_ctx_ok(const char * file, int line)
     {
         if (nix_err_code(ctx) == NIX_OK) {
             return;
@@ -32,16 +38,18 @@ protected:
         unsigned int n;
         const char * p = nix_err_msg(nullptr, ctx, &n);
         std::string msg(p, n);
-        throw std::runtime_error(std::string("nix_err_code(ctx) != NIX_OK, message: ") + msg);
+        throw std::runtime_error(loc(file, line) + ": nix_err_code(ctx) != NIX_OK, message: " + msg);
     }
+#define assert_ctx_ok() assert_ctx_ok(__FILE__, __LINE__)
 
-    inline void assert_ctx_err()
+    inline void assert_ctx_err(const char * file, int line)
     {
         if (nix_err_code(ctx) != NIX_OK) {
             return;
         }
-        throw std::runtime_error("Got NIX_OK, but expected an error!");
+        throw std::runtime_error(loc(file, line) + ": Got NIX_OK, but expected an error!");
     }
+#define assert_ctx_err() assert_ctx_err(__FILE__, __LINE__)
 };
 
 }