diff --git a/src/libmain/common-args.cc b/src/libmain/common-args.cc
index d3aac6ab..bcc05c2c 100644
--- a/src/libmain/common-args.cc
+++ b/src/libmain/common-args.cc
@@ -37,6 +37,10 @@ MixCommonArgs::MixCommonArgs(const string & programName)
 
     std::string cat = "config";
     settings.convertToArgs(*this, cat);
+
+    // Backward compatibility hack: nix-env already had a --system flag.
+    if (programName == "nix-env") longFlags.erase("system");
+
     hiddenCategories.insert(cat);
 }
 
diff --git a/tests/user-envs.sh b/tests/user-envs.sh
index c4192fdc..ba639231 100644
--- a/tests/user-envs.sh
+++ b/tests/user-envs.sh
@@ -24,6 +24,9 @@ rm -f $HOME/.nix-defexpr
 ln -s $(pwd)/user-envs.nix $HOME/.nix-defexpr
 nix-env -qa '*' --description | grep -q silly
 
+# Query the system.
+nix-env -qa '*' --system | grep -q $system
+
 # Install "foo-1.0".
 nix-env -i foo-1.0