diff --git a/lix/libexpr/flake/flakeref.cc b/lix/libexpr/flake/flakeref.cc
index a26ce741e..663c637c8 100644
--- a/lix/libexpr/flake/flakeref.cc
+++ b/lix/libexpr/flake/flakeref.cc
@@ -1,5 +1,6 @@
 #include "lix/libexpr/flake/flakeref.hh"
 #include "lix/libstore/store-api.hh"
+#include "lix/libutil/async.hh"
 #include "lix/libutil/url.hh"
 #include "lix/libutil/url-parts.hh"
 #include "lix/libfetchers/fetchers.hh"
@@ -239,7 +240,7 @@ FlakeRef FlakeRef::fromAttrs(const fetchers::Attrs & attrs)
 
 std::pair<fetchers::Tree, FlakeRef> FlakeRef::fetchTree(ref<Store> store) const
 {
-    auto [tree, lockedInput] = input.fetch(store);
+    auto [tree, lockedInput] = RUN_ASYNC_IN_NEW_THREAD(input.fetch(store));
     return {std::move(tree), FlakeRef(std::move(lockedInput), subdir)};
 }
 
diff --git a/lix/libexpr/primops/fetchMercurial.cc b/lix/libexpr/primops/fetchMercurial.cc
index 45f2588d9..db89cd131 100644
--- a/lix/libexpr/primops/fetchMercurial.cc
+++ b/lix/libexpr/primops/fetchMercurial.cc
@@ -65,7 +65,7 @@ static void prim_fetchMercurial(EvalState & state, const PosIdx pos, Value * * a
     auto input = fetchers::Input::fromAttrs(std::move(attrs));
 
     // FIXME: use name
-    auto [tree, input2] = input.fetch(state.ctx.store);
+    auto [tree, input2] = state.aio.blockOn(input.fetch(state.ctx.store));
 
     auto attrs2 = state.ctx.buildBindings(8);
     state.ctx.paths.mkStorePathString(tree.storePath, attrs2.alloc(state.ctx.s.outPath));
diff --git a/lix/libexpr/primops/fetchTree.cc b/lix/libexpr/primops/fetchTree.cc
index c81d5ae91..8c3348496 100644
--- a/lix/libexpr/primops/fetchTree.cc
+++ b/lix/libexpr/primops/fetchTree.cc
@@ -192,7 +192,7 @@ static void fetchTree(
         state.ctx.errors.make<EvalError>("in pure evaluation mode, 'fetchTree' requires a locked input").atPos(pos).debugThrow();
     }
 
-    auto [tree, input2] = input.fetch(state.ctx.store);
+    auto [tree, input2] = state.aio.blockOn(input.fetch(state.ctx.store));
 
     state.ctx.paths.allowPath(tree.storePath);
 
diff --git a/lix/libfetchers/fetchers.cc b/lix/libfetchers/fetchers.cc
index 866794f9c..703e30bce 100644
--- a/lix/libfetchers/fetchers.cc
+++ b/lix/libfetchers/fetchers.cc
@@ -123,8 +123,8 @@ bool Input::contains(const Input & other) const
     return false;
 }
 
-std::pair<Tree, Input> Input::fetch(ref<Store> store) const
-{
+kj::Promise<Result<std::pair<Tree, Input>>> Input::fetch(ref<Store> store) const
+try {
     if (!scheme)
         throw Error("cannot fetch unsupported input '%s'", attrsToJSON(toAttrs()));
 
@@ -135,12 +135,15 @@ std::pair<Tree, Input> Input::fetch(ref<Store> store) const
         try {
             auto storePath = computeStorePath(*store);
 
-            RUN_ASYNC_IN_NEW_THREAD(store->ensurePath(storePath));
+            TRY_AWAIT(store->ensurePath(storePath));
 
             debug("using substituted/cached input '%s' in '%s'",
                 to_string(), store->printStorePath(storePath));
 
-            return {Tree { .actualPath = store->toRealPath(storePath), .storePath = std::move(storePath) }, *this};
+            co_return {
+                Tree{.actualPath = store->toRealPath(storePath), .storePath = std::move(storePath)},
+                *this
+            };
         } catch (Error & e) {
             debug("substitution of input '%s' failed: %s", to_string(), e.what());
         }
@@ -197,7 +200,9 @@ std::pair<Tree, Input> Input::fetch(ref<Store> store) const
 
     assert(input.hasAllInfo());
 
-    return {std::move(tree), input};
+    co_return {std::move(tree), input};
+} catch (...) {
+    co_return result::current_exception();
 }
 
 Input Input::applyOverrides(
diff --git a/lix/libfetchers/fetchers.hh b/lix/libfetchers/fetchers.hh
index 6854c1b92..4393b78c1 100644
--- a/lix/libfetchers/fetchers.hh
+++ b/lix/libfetchers/fetchers.hh
@@ -1,6 +1,7 @@
 #pragma once
 ///@file
 
+#include "lix/libutil/result.hh"
 #include "lix/libutil/types.hh"
 #include "lix/libutil/hash.hh"
 #include "lix/libutil/canon-path.hh"
@@ -10,6 +11,7 @@
 #include "lix/libutil/ref.hh"
 #include "lix/libutil/strings.hh"
 
+#include <kj/async.h>
 #include <memory>
 
 namespace nix { class Store; }
@@ -90,7 +92,7 @@ public:
      * Fetch the input into the Nix store, returning the location in
      * the Nix store and the locked input.
      */
-    std::pair<Tree, Input> fetch(ref<Store> store) const;
+    kj::Promise<Result<std::pair<Tree, Input>>> fetch(ref<Store> store) const;
 
     Input applyOverrides(
         std::optional<std::string> ref,
diff --git a/lix/nix/flake.cc b/lix/nix/flake.cc
index 7c65ffb16..2b45504dd 100644
--- a/lix/nix/flake.cc
+++ b/lix/nix/flake.cc
@@ -1070,7 +1070,7 @@ struct CmdFlakeArchive : FlakeCommand, MixJSON, MixDryRun
                     auto storePath =
                         dryRun
                         ? (*inputNode)->lockedRef.input.computeStorePath(*store)
-                        : (*inputNode)->lockedRef.input.fetch(store).first.storePath;
+                        : aio().blockOn((*inputNode)->lockedRef.input.fetch(store)).first.storePath;
                     if (json) {
                         auto& jsonObj3 = jsonObj2[inputName];
                         jsonObj3["path"] = store->printStorePath(storePath);
diff --git a/lix/nix/registry.cc b/lix/nix/registry.cc
index 324af5000..caba6849f 100644
--- a/lix/nix/registry.cc
+++ b/lix/nix/registry.cc
@@ -196,7 +196,7 @@ struct CmdRegistryPin : RegistryCommand, EvalCommand
         auto ref = parseFlakeRef(url);
         auto lockedRef = parseFlakeRef(locked);
         registry->remove(ref.input);
-        auto [tree, resolved] = lockedRef.resolve(store).input.fetch(store);
+        auto [tree, resolved] = aio().blockOn(lockedRef.resolve(store).input.fetch(store));
         fetchers::Attrs extraAttrs;
         if (ref.subdir != "") extraAttrs["dir"] = ref.subdir;
         registry->add(ref.input, resolved, extraAttrs);