diff --git a/corepkgs/default-installation-source.nix b/corepkgs/default-installation-source.nix
deleted file mode 100644
index 71ba04452..000000000
--- a/corepkgs/default-installation-source.nix
+++ /dev/null
@@ -1,3 +0,0 @@
-builtins.mapAttrs (flakeName: flakeInfo:
-  (getFlake flakeInfo.uri).${flakeName}.provides.packages or {})
-  builtins.flakeRegistry
diff --git a/corepkgs/local.mk b/corepkgs/local.mk
index 41aaec63b..67306e50d 100644
--- a/corepkgs/local.mk
+++ b/corepkgs/local.mk
@@ -3,8 +3,7 @@ corepkgs_FILES = \
   unpack-channel.nix \
   derivation.nix \
   fetchurl.nix \
-  imported-drv-to-derivation.nix \
-  default-installation-source.nix
+  imported-drv-to-derivation.nix
 
 $(foreach file,config.nix $(corepkgs_FILES),$(eval $(call install-data-in,$(d)/$(file),$(datadir)/nix/corepkgs)))
 
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 35c01b97a..27c6c3da8 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -318,6 +318,8 @@ public:
 
     const FlakeRegistry & getFlakeRegistry();
 
+    Value * makeFlakeRegistryValue();
+
 private:
     std::unique_ptr<FlakeRegistry> _flakeRegistry;
     std::once_flag _flakeRegistryInit;
diff --git a/src/libexpr/primops/flake.cc b/src/libexpr/primops/flake.cc
index 5e92b1da3..4d027558d 100644
--- a/src/libexpr/primops/flake.cc
+++ b/src/libexpr/primops/flake.cc
@@ -16,50 +16,49 @@ const FlakeRegistry & EvalState::getFlakeRegistry()
     {
         _flakeRegistry = std::make_unique<FlakeRegistry>();
 
-        if (!evalSettings.pureEval) {
-
 #if 0
-            auto registryUri = "file:///home/eelco/Dev/gists/nix-flakes/registry.json";
+        auto registryUri = "file:///home/eelco/Dev/gists/nix-flakes/registry.json";
 
-            auto registryFile = getDownloader()->download(DownloadRequest(registryUri));
+        auto registryFile = getDownloader()->download(DownloadRequest(registryUri));
 #endif
 
-            auto registryFile = readFile(settings.nixDataDir + "/nix/flake-registry.json");
+        auto registryFile = readFile(settings.nixDataDir + "/nix/flake-registry.json");
 
-            auto json = nlohmann::json::parse(registryFile);
+        auto json = nlohmann::json::parse(registryFile);
 
-            auto version = json.value("version", 0);
-            if (version != 1)
-                throw Error("flake registry '%s' has unsupported version %d", registryFile, version);
+        auto version = json.value("version", 0);
+        if (version != 1)
+            throw Error("flake registry '%s' has unsupported version %d", registryFile, version);
 
-            auto flakes = json["flakes"];
-            for (auto i = flakes.begin(); i != flakes.end(); ++i) {
-                FlakeRegistry::Entry entry{FlakeRef(i->value("uri", ""))};
-                _flakeRegistry->entries.emplace(i.key(), entry);
-            }
+        auto flakes = json["flakes"];
+        for (auto i = flakes.begin(); i != flakes.end(); ++i) {
+            FlakeRegistry::Entry entry{FlakeRef(i->value("uri", ""))};
+            _flakeRegistry->entries.emplace(i.key(), entry);
         }
     });
 
     return *_flakeRegistry;
 }
 
-static void prim_flakeRegistry(EvalState & state, const Pos & pos, Value * * args, Value & v)
+Value * EvalState::makeFlakeRegistryValue()
 {
-    auto registry = state.getFlakeRegistry();
+    auto v = allocValue();
 
-    state.mkAttrs(v, registry.entries.size());
+    auto registry = getFlakeRegistry();
+
+    mkAttrs(*v, registry.entries.size());
 
     for (auto & entry : registry.entries) {
-        auto vEntry = state.allocAttr(v, entry.first);
-        state.mkAttrs(*vEntry, 2);
-        mkString(*state.allocAttr(*vEntry, state.symbols.create("uri")), entry.second.ref.to_string());
+        auto vEntry = allocAttr(*v, entry.first);
+        mkAttrs(*vEntry, 2);
+        mkString(*allocAttr(*vEntry, symbols.create("uri")), entry.second.ref.to_string());
         vEntry->attrs->sort();
     }
 
-    v.attrs->sort();
-}
+    v->attrs->sort();
 
-static RegisterPrimOp r1("__flakeRegistry", 0, prim_flakeRegistry);
+    return v;
+}
 
 static FlakeRef lookupFlake(EvalState & state, const FlakeRef & flakeRef)
 {
@@ -129,6 +128,9 @@ static Flake getFlake(EvalState & state, const FlakeRef & flakeRef)
     auto flakePath = fetchFlake(state, flakeRef);
     state.store->assertStorePath(flakePath);
 
+    if (state.allowedPaths)
+        state.allowedPaths->insert(flakePath);
+
     Flake flake;
 
     Value vInfo;
diff --git a/src/nix/installables.cc b/src/nix/installables.cc
index 9b7b96c25..faad057a7 100644
--- a/src/nix/installables.cc
+++ b/src/nix/installables.cc
@@ -30,8 +30,15 @@ Value * SourceExprCommand::getSourceExpr(EvalState & state)
 
     if (file != "")
         state.evalFile(lookupFileArg(state, file), *vSourceExpr);
-    else
-        state.evalFile(lookupFileArg(state, "<nix/default-installation-source.nix>"), *vSourceExpr);
+    else {
+        auto fun = state.parseExprFromString(
+             "builtins.mapAttrs (flakeName: flakeInfo:"
+             "  (getFlake flakeInfo.uri).${flakeName}.provides.packages or {})", "/");
+        auto vFun = state.allocValue();
+        state.eval(fun, *vFun);
+        auto vRegistry = state.makeFlakeRegistryValue();
+        mkApp(*vSourceExpr, *vFun, *vRegistry);
+    }
 
     return vSourceExpr;
 }
diff --git a/src/nix/main.cc b/src/nix/main.cc
index 4b909736d..01b0866f2 100644
--- a/src/nix/main.cc
+++ b/src/nix/main.cc
@@ -97,6 +97,7 @@ void mainWrapped(int argc, char * * argv)
 
     verbosity = lvlError;
     settings.verboseBuild = false;
+    evalSettings.pureEval = true;
 
     NixArgs args;