diff --git a/src/libutil/experimental-features.cc b/src/libutil/experimental-features.cc
index 11b8ceadf..198d021bb 100644
--- a/src/libutil/experimental-features.cc
+++ b/src/libutil/experimental-features.cc
@@ -383,6 +383,7 @@ MissingExperimentalFeature::MissingExperimentalFeature(ExperimentalFeature featu
           showExperimentalFeature(feature),
           Uncolored(optionalBracket(" (", reason, ")")))
     , missingFeature(feature)
+    , reason{reason}
 {
 }
 
diff --git a/src/libutil/include/nix/util/experimental-features.hh b/src/libutil/include/nix/util/experimental-features.hh
index 6ffc0e0c0..aca14bfbb 100644
--- a/src/libutil/include/nix/util/experimental-features.hh
+++ b/src/libutil/include/nix/util/experimental-features.hh
@@ -88,6 +88,8 @@ public:
      */
     ExperimentalFeature missingFeature;
 
+    std::string reason;
+
     MissingExperimentalFeature(ExperimentalFeature missingFeature, std::string reason = "");
 };