diff --git a/lix/libfetchers/cache.cc b/lix/libfetchers/cache.cc
index 3f9f4fb65..b225928bf 100644
--- a/lix/libfetchers/cache.cc
+++ b/lix/libfetchers/cache.cc
@@ -1,10 +1,12 @@
 #include "lix/libfetchers/cache.hh"
 #include "lix/libstore/sqlite.hh"
+#include "lix/libutil/async.hh"
 #include "lix/libutil/sync.hh"
 #include "lix/libstore/store-api.hh"
 #include "lix/libutil/users.hh"
 
 #include <nlohmann/json.hpp>
+#include <optional>
 
 namespace nix::fetchers {
 
@@ -72,23 +74,25 @@ struct CacheImpl : Cache
             (time(0)).exec();
     }
 
-    std::optional<std::pair<Attrs, StorePath>> lookup(
+    kj::Promise<Result<std::optional<std::pair<Attrs, StorePath>>>> lookup(
         ref<Store> store,
         const Attrs & inAttrs) override
-    {
-        if (auto res = lookupExpired(store, inAttrs)) {
+    try {
+        if (auto res = TRY_AWAIT(lookupExpired(store, inAttrs))) {
             if (!res->expired)
-                return std::make_pair(std::move(res->infoAttrs), std::move(res->storePath));
+                co_return std::make_pair(std::move(res->infoAttrs), std::move(res->storePath));
             debug("ignoring expired cache entry '%s'",
                 attrsToJSON(inAttrs).dump());
         }
-        return {};
+        co_return std::nullopt;
+    } catch (...) {
+        co_return result::current_exception();
     }
 
-    std::optional<Result> lookupExpired(
+    kj::Promise<Result<std::optional<LookupResult>>> lookupExpired(
         ref<Store> store,
         const Attrs & inAttrs) override
-    {
+    try {
         auto state(_state.lock());
 
         auto inAttrsJSON = attrsToJSON(inAttrs).dump();
@@ -96,7 +100,7 @@ struct CacheImpl : Cache
         auto stmt(state->lookup.use()(inAttrsJSON));
         if (!stmt.next()) {
             debug("did not find cache entry for '%s'", inAttrsJSON);
-            return {};
+            co_return std::nullopt;
         }
 
         auto infoJSON = stmt.getStr(0);
@@ -108,17 +112,19 @@ struct CacheImpl : Cache
         if (!store->isValidPath(storePath)) {
             // FIXME: we could try to substitute 'storePath'.
             debug("ignoring disappeared cache entry '%s'", inAttrsJSON);
-            return {};
+            co_return std::nullopt;
         }
 
         debug("using cache entry '%s' -> '%s', '%s'",
             inAttrsJSON, infoJSON, store->printStorePath(storePath));
 
-        return Result {
+        co_return LookupResult {
             .expired = !locked && (settings.tarballTtl.get() == 0 || timestamp + settings.tarballTtl < time(0)),
             .infoAttrs = jsonToAttrs(nlohmann::json::parse(infoJSON)),
             .storePath = std::move(storePath)
         };
+    } catch (...) {
+        co_return result::current_exception();
     }
 };
 
diff --git a/lix/libfetchers/cache.hh b/lix/libfetchers/cache.hh
index 91af2d80a..5379b5fd4 100644
--- a/lix/libfetchers/cache.hh
+++ b/lix/libfetchers/cache.hh
@@ -17,18 +17,18 @@ struct Cache
         const StorePath & storePath,
         bool locked) = 0;
 
-    virtual std::optional<std::pair<Attrs, StorePath>> lookup(
+    virtual kj::Promise<Result<std::optional<std::pair<Attrs, StorePath>>>> lookup(
         ref<Store> store,
         const Attrs & inAttrs) = 0;
 
-    struct Result
+    struct LookupResult
     {
         bool expired = false;
         Attrs infoAttrs;
         StorePath storePath;
     };
 
-    virtual std::optional<Result> lookupExpired(
+    virtual kj::Promise<Result<std::optional<LookupResult>>> lookupExpired(
         ref<Store> store,
         const Attrs & inAttrs) = 0;
 };
diff --git a/lix/libfetchers/git.cc b/lix/libfetchers/git.cc
index 7240fba07..ec9285f67 100644
--- a/lix/libfetchers/git.cc
+++ b/lix/libfetchers/git.cc
@@ -491,7 +491,7 @@ struct GitInputScheme : InputScheme
         };
 
         if (input.getRev()) {
-            if (auto res = getCache()->lookup(store, getLockedAttrs()))
+            if (auto res = TRY_AWAIT(getCache()->lookup(store, getLockedAttrs())))
                 co_return makeResult(res->first, std::move(res->second));
         }
 
@@ -547,7 +547,7 @@ struct GitInputScheme : InputScheme
                 }
             }
 
-            if (auto res = getCache()->lookup(store, unlockedAttrs)) {
+            if (auto res = TRY_AWAIT(getCache()->lookup(store, unlockedAttrs))) {
                 auto rev2 = Hash::parseAny(getStrAttr(res->first, "rev"), HashType::SHA1);
                 if (!input.getRev() || input.getRev() == rev2) {
                     input.attrs.insert_or_assign("rev", rev2.gitRev());
@@ -686,7 +686,7 @@ struct GitInputScheme : InputScheme
 
         /* Now that we know the ref, check again whether we have it in
            the store. */
-        if (auto res = getCache()->lookup(store, getLockedAttrs()))
+        if (auto res = TRY_AWAIT(getCache()->lookup(store, getLockedAttrs())))
             co_return makeResult(res->first, std::move(res->second));
 
         Path tmpDir = createTempDir();
diff --git a/lix/libfetchers/mercurial.cc b/lix/libfetchers/mercurial.cc
index 9e20c29a7..623cf9d36 100644
--- a/lix/libfetchers/mercurial.cc
+++ b/lix/libfetchers/mercurial.cc
@@ -1,6 +1,7 @@
 #include "lix/libfetchers/fetchers.hh"
 #include "lix/libfetchers/cache.hh"
 #include "lix/libfetchers/builtin-fetchers.hh"
+#include "lix/libutil/async.hh"
 #include "lix/libutil/processes.hh"
 #include "lix/libstore/store-api.hh"
 #include "lix/libstore/temporary-dir.hh"
@@ -243,7 +244,7 @@ struct MercurialInputScheme : InputScheme
         };
 
         if (input.getRev()) {
-            if (auto res = getCache()->lookup(store, getLockedAttrs()))
+            if (auto res = TRY_AWAIT(getCache()->lookup(store, getLockedAttrs())))
                 co_return makeResult(res->first, std::move(res->second));
         }
 
@@ -256,7 +257,7 @@ struct MercurialInputScheme : InputScheme
             {"ref", *input.getRef()},
         });
 
-        if (auto res = getCache()->lookup(store, unlockedAttrs)) {
+        if (auto res = TRY_AWAIT(getCache()->lookup(store, unlockedAttrs))) {
             auto rev2 = Hash::parseAny(getStrAttr(res->first, "rev"), HashType::SHA1);
             if (!input.getRev() || input.getRev() == rev2) {
                 input.attrs.insert_or_assign("rev", rev2.gitRev());
@@ -302,7 +303,7 @@ struct MercurialInputScheme : InputScheme
         auto revCount = std::stoull(tokens[1]);
         input.attrs.insert_or_assign("ref", tokens[2]);
 
-        if (auto res = getCache()->lookup(store, getLockedAttrs()))
+        if (auto res = TRY_AWAIT(getCache()->lookup(store, getLockedAttrs())))
             co_return makeResult(res->first, std::move(res->second));
 
         Path tmpDir = createTempDir();
diff --git a/lix/libfetchers/tarball.cc b/lix/libfetchers/tarball.cc
index 1d05a4642..201552b77 100644
--- a/lix/libfetchers/tarball.cc
+++ b/lix/libfetchers/tarball.cc
@@ -28,7 +28,7 @@ try {
         {"name", name},
     });
 
-    auto cached = getCache()->lookupExpired(store, inAttrs);
+    auto cached = TRY_AWAIT(getCache()->lookupExpired(store, inAttrs));
 
     auto useCached = [&]() -> DownloadFileResult
     {
@@ -135,7 +135,7 @@ try {
         {"name", name},
     });
 
-    auto cached = getCache()->lookupExpired(store, inAttrs);
+    auto cached = TRY_AWAIT(getCache()->lookupExpired(store, inAttrs));
 
     if (cached && !cached->expired)
         co_return DownloadTarballResult{