diff --git a/ktor-client/ktor-client-curl/desktop/src/io/ktor/client/engine/curl/internal/CurlCallbacks.kt b/ktor-client/ktor-client-curl/desktop/src/io/ktor/client/engine/curl/internal/CurlCallbacks.kt
index 6b41b7a163a..b2f31182ed4 100644
--- a/ktor-client/ktor-client-curl/desktop/src/io/ktor/client/engine/curl/internal/CurlCallbacks.kt
+++ b/ktor-client/ktor-client-curl/desktop/src/io/ktor/client/engine/curl/internal/CurlCallbacks.kt
@@ -55,7 +55,7 @@ internal fun onBodyChunkReceived(
         return -1
     }
     if (written > 0) {
-        wrapper.bytesWritten += written
+        wrapper.bytesWritten.addAndGet(written)
     }
     if (wrapper.bytesWritten.value == chunkSize) {
         wrapper.bytesWritten.value = 0