diff --git a/corepkgs/buildenv.nix b/corepkgs/buildenv.nix
index 92377837..c52a0ea9 100644
--- a/corepkgs/buildenv.nix
+++ b/corepkgs/buildenv.nix
@@ -13,7 +13,7 @@ derivation {
   # !!! grmbl, need structured data for passing this in a clean way.
   derivations =
     map (d:
-      [ (if d.meta.active or true then "1" else "0")
+      [ (d.meta.active or "true")
         (d.meta.priority or 5)
         (builtins.length d.outputs)
       ] ++ map (output: builtins.getAttr output d) d.outputs)
diff --git a/corepkgs/buildenv.pl b/corepkgs/buildenv.pl
index 3d79e503..ea517687 100644
--- a/corepkgs/buildenv.pl
+++ b/corepkgs/buildenv.pl
@@ -134,7 +134,7 @@ while (scalar @derivations) {
     for (my $n = 0; $n < $outputs; $n++) {
         my $path = shift @derivations;
         $pkgs{$path} =
-            { active => int($active)
+            { active => $active ne "false"
             , priority => int($priority) };
     }
 }
diff --git a/tests/user-envs.sh b/tests/user-envs.sh
index 2bc9bee5..465d2fc5 100644
--- a/tests/user-envs.sh
+++ b/tests/user-envs.sh
@@ -22,6 +22,14 @@ test "$(nix-env -p $profiles/test -q '*' | wc -l)" -eq 1
 nix-env -p $profiles/test -q '*' | grep -q foo-1.0
 test "$($profiles/test/bin/foo)" = "foo-1.0"
 
+# Disable foo.
+nix-env -p $profiles/test --set-flag active false foo
+! [ -e "$profiles/test/bin/foo" ]
+
+# Enable foo.
+nix-env -p $profiles/test --set-flag active true foo
+[ -e "$profiles/test/bin/foo" ]
+
 # Store the path of foo-1.0.
 outPath10=$(nix-env -p $profiles/test -q --out-path --no-name '*' | grep foo-1.0)
 echo "foo-1.0 = $outPath10"
@@ -67,7 +75,7 @@ if nix-env -p $profiles/test -q '*' | grep -q bar; then false; fi
 
 # Count generations.
 nix-env -p $profiles/test --list-generations
-test "$(nix-env -p $profiles/test --list-generations | wc -l)" -eq 5
+test "$(nix-env -p $profiles/test --list-generations | wc -l)" -eq 7
 
 # Install foo-1.0, now using its store path.
 echo $outPath10