diff --git a/release.nix b/release.nix
index 04f1f8367..bdac283cf 100644
--- a/release.nix
+++ b/release.nix
@@ -6,7 +6,7 @@
 
 let
 
-  pkgs = import nixpkgs { system = "x86_64-linux"; };
+  pkgs = import nixpkgs { system = builtins.currentSystem or "x86_64-linux"; };
 
   jobs = rec {
 
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index e90a1da25..975f0e830 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -1997,16 +1997,12 @@ void EvalState::createBaseEnv()
         addConstant(name, v);
     };
 
-    if (settings.pureEval)
-        addPurityError("__currentTime");
-    else {
+    if (!settings.pureEval) {
         mkInt(v, time(0));
         addConstant("__currentTime", v);
     }
 
-    if (settings.pureEval)
-        addPurityError("__currentSystem");
-    else {
+    if (!settings.pureEval) {
         mkString(v, settings.thisSystem);
         addConstant("__currentSystem", v);
     }