diff --git a/src/libutil-test-support/include/nix/util/tests/characterization.hh b/src/libutil-test-support/include/nix/util/tests/characterization.hh
index d8fad1df9..67ad8fb51 100644
--- a/src/libutil-test-support/include/nix/util/tests/characterization.hh
+++ b/src/libutil-test-support/include/nix/util/tests/characterization.hh
@@ -15,7 +15,11 @@ namespace nix {
  */
 static inline std::filesystem::path getUnitTestData()
 {
-    return getEnv("_NIX_TEST_UNIT_DATA").value();
+    auto data = getEnv("_NIX_TEST_UNIT_DATA");
+    if (!data)
+        throw Error(
+            "_NIX_TEST_UNIT_DATA environment variable is not set. Recommendation: use meson, example: 'meson test -C build --gdb'");
+    return std::filesystem::path(*data);
 }
 
 /**