diff --git a/plugins/preprocess/preprocess_node.cpp b/plugins/preprocess/preprocess_node.cpp
index 1e91fd4..3b99166 100644
--- a/plugins/preprocess/preprocess_node.cpp
+++ b/plugins/preprocess/preprocess_node.cpp
@@ -360,10 +360,14 @@ private:
                 std::cerr << "[preprocess] DMA alloc for src failed\n";
                 return false;
             }
+            // CPU writes to a DMA-BUF must be flushed before RGA reads it.
+            DmaSyncStartFd(src_dma_buf->fd);
             if (!CopyToStridedBuffer(*frame, src_dma_buf->data(), src_dma_buf->size, src_wstride, src_hstride)) {
+                DmaSyncEndFd(src_dma_buf->fd);
                 std::cerr << "[preprocess] copy src to DMA failed\n";
                 return false;
             }
+            DmaSyncEndFd(src_dma_buf->fd);
             src_buf = wrapbuffer_fd_t(src_dma_buf->fd, frame->width, frame->height,
                                       src_wstride, src_hstride, src_fmt_rga);
         } else {