diff --git a/src/libutil/args.hh b/src/libutil/args.hh
index 7f8ea647c..401bebbab 100644
--- a/src/libutil/args.hh
+++ b/src/libutil/args.hh
@@ -81,15 +81,16 @@ public:
         FlagMaker & handler(std::function<void(Strings)> handler) { flag->handler = handler; return *this; };
         FlagMaker & category(const std::string & s) { flag->category = s; return *this; };
 
-        FlagMaker & dest(std::string * dest) {
-            assert(flag->arity == 1);
+        template<class T>
+        FlagMaker & dest(T * dest) {
+            flag->arity = 1;
             flag->handler = [=](Strings ss) { *dest = ss.front(); };
             return *this;
         };
 
         template<class T>
         FlagMaker & set(T * dest, const T & val) {
-            assert(flag->arity == 0);
+            flag->arity = 1;
             flag->handler = [=](Strings ss) { *dest = val; };
             return *this;
         };
diff --git a/src/nix/add-to-store.cc b/src/nix/add-to-store.cc
new file mode 100644
index 000000000..d0003790d
--- /dev/null
+++ b/src/nix/add-to-store.cc
@@ -0,0 +1,61 @@
+#include "command.hh"
+#include "common-args.hh"
+#include "store-api.hh"
+#include "archive.hh"
+
+using namespace nix;
+
+struct CmdAddToStore : MixDryRun, StoreCommand
+{
+    Path path;
+    std::experimental::optional<std::string> namePart;
+
+    CmdAddToStore()
+    {
+        expectArg("path", &path);
+
+        mkFlag()
+            .longName("name")
+            .shortName('n')
+            .description("name component of the store path")
+            .labels({"name"})
+            .dest(&namePart);
+    }
+
+    std::string name() override
+    {
+        return "add-to-store";
+    }
+
+    std::string description() override
+    {
+        return "add a path to the Nix store";
+    }
+
+    Examples examples() override
+    {
+        return {
+        };
+    }
+
+    void run(ref<Store> store) override
+    {
+        if (!namePart) namePart = baseNameOf(path);
+
+        StringSink sink;
+        dumpPath(path, sink);
+
+        ValidPathInfo info;
+        info.narHash = hashString(htSHA256, *sink.s);
+        info.narSize = sink.s->size();
+        info.path = store->makeFixedOutputPath(true, info.narHash, *namePart);
+        info.ca = makeFixedOutputCA(true, info.narHash);
+
+        if (!dryRun)
+            store->addToStore(info, sink.s);
+
+        std::cout << fmt("%s\n", info.path);
+    }
+};
+
+static RegisterCommand r1(make_ref<CmdAddToStore>());
diff --git a/src/nix/build.cc b/src/nix/build.cc
index 915a06649..f7c99f12d 100644
--- a/src/nix/build.cc
+++ b/src/nix/build.cc
@@ -15,7 +15,6 @@ struct CmdBuild : MixDryRun, InstallablesCommand
             .longName("out-link")
             .shortName('o')
             .description("path of the symlink to the build result")
-            .arity(1)
             .labels({"path"})
             .dest(&outLink);
 
diff --git a/src/nix/why-depends.cc b/src/nix/why-depends.cc
index f31469cbc..a90d07ed2 100644
--- a/src/nix/why-depends.cc
+++ b/src/nix/why-depends.cc
@@ -233,6 +233,8 @@ struct CmdWhyDepends : SourceExprCommand
                 }
             };
 
+            // FIXME: should use scanForReferences().
+
             visitPath(node.path);
 
             for (auto & ref : refs) {