diff --git a/src/libexpr/flake/flake.cc b/src/libexpr/flake/flake.cc
index 2c51f8752..e573e53b4 100644
--- a/src/libexpr/flake/flake.cc
+++ b/src/libexpr/flake/flake.cc
@@ -659,9 +659,9 @@ LockedFlake lockFlake(
                                 if (s.empty())
                                     warn("updating lock file '%s'", outputLockFilePath);
                                 else
-                                    warn("updating lock file '%s':\n%s", outputLockFilePath, s);
+                                    warn("updating lock file '%s':\n%s", outputLockFilePath, Uncolored(s));
                             } else
-                                warn("creating lock file '%s':\n%s", outputLockFilePath, s);
+                                warn("creating lock file '%s':\n%s", outputLockFilePath, Uncolored(s));
 
                             std::optional<std::string> commitMessage = std::nullopt;