diff --git a/src/hydra-queue-runner/builder.cc b/src/hydra-queue-runner/builder.cc
index 4d46457b..20451953 100644
--- a/src/hydra-queue-runner/builder.cc
+++ b/src/hydra-queue-runner/builder.cc
@@ -154,7 +154,7 @@ State::StepResult State::doBuildStep(nix::ref<Store> destStore,
             try {
                 auto store = destStore.dynamic_pointer_cast<BinaryCacheStore>();
                 if (uploadLogsToBinaryCache && store && pathExists(result.logFile)) {
-                    store->upsertFile("log/" + baseNameOf(buildDrvPath), readFile(result.logFile), "text/plain");
+                    store->upsertFile("log/" + baseNameOf(buildDrvPath), readFile(result.logFile), "text/plain; charset=utf-8");
                     unlink(result.logFile.c_str());
                 }
             } catch (...) {