diff --git a/src/nix/upgrade-nix.cc b/src/nix/upgrade-nix.cc
index a4722abf5..77fb798a7 100644
--- a/src/nix/upgrade-nix.cc
+++ b/src/nix/upgrade-nix.cc
@@ -126,7 +126,7 @@ struct CmdUpgradeNix : MixDryRun, StoreCommand
 
         if (where.filename() != "bin" ||
             !hasSuffix(userEnv, "user-environment"))
-            throw Error("directory '%s' does not appear to be part of a Nix profile", where);
+            throw Error("directory %s does not appear to be part of a Nix profile", where);
 
         if (!store->isValidPath(store->parseStorePath(userEnv)))
             throw Error("directory '%s' is not in the Nix store", userEnv);