diff --git a/src/nix/installables.cc b/src/nix/installables.cc
index 071edf432..3bf4fa8f4 100644
--- a/src/nix/installables.cc
+++ b/src/nix/installables.cc
@@ -454,7 +454,7 @@ std::vector<std::shared_ptr<Installable>> SourceExprCommand::parseInstallables(
         for (auto & s : ss) {
             if (hasPrefix(s, "nixpkgs.")) {
                 bool static warned;
-                warnOnce(warned, "the syntax 'nixpkgs.<attr>' is deprecated; use 'nixpkgs:<attr>' instead");
+                warnOnce(warned, "the syntax 'nixpkgs.<attr>' is deprecated; use 'nixpkgs#<attr>' instead");
                 result.push_back(std::make_shared<InstallableFlake>(*this,
                         FlakeRef::fromAttrs({{"type", "indirect"}, {"id", "nixpkgs"}}),
                         Strings{"legacyPackages." + settings.thisSystem.get() + "." + std::string(s, 8)}, Strings{}));