diff --git a/hw/xbox/nv2a/pgraph/vk/vertex.c b/hw/xbox/nv2a/pgraph/vk/vertex.c
index b7bf97b38a..60154cf0d1 100644
--- a/hw/xbox/nv2a/pgraph/vk/vertex.c
+++ b/hw/xbox/nv2a/pgraph/vk/vertex.c
@@ -49,9 +49,12 @@ void pgraph_vk_update_vertex_ram_buffer(PGRAPHState *pg, hwaddr offset,
 
     pgraph_vk_download_surfaces_in_range_if_dirty(pg, offset, size);
 
-    size_t offset_bit = offset / 4096;
-    size_t nbits = size / 4096;
-    if (find_next_bit(r->uploaded_bitmap, nbits, offset_bit) < nbits) {
+    size_t start_bit = offset / TARGET_PAGE_SIZE;
+    size_t end_bit = TARGET_PAGE_ALIGN(offset + size) / TARGET_PAGE_SIZE;
+    size_t nbits = end_bit - start_bit;
+
+    if (find_next_bit(r->uploaded_bitmap, start_bit + nbits, start_bit) <
+        end_bit) {
         // Vertex data changed while building the draw list. Finish drawing
         // before updating RAM buffer.
         pgraph_vk_finish(pg, VK_FINISH_REASON_VERTEX_BUFFER_DIRTY);
@@ -60,7 +63,7 @@ void pgraph_vk_update_vertex_ram_buffer(PGRAPHState *pg, hwaddr offset,
     nv2a_profile_inc_counter(NV2A_PROF_GEOM_BUFFER_UPDATE_1);
     memcpy(r->storage_buffers[BUFFER_VERTEX_RAM].mapped + offset, data, size);
 
-    bitmap_set(r->uploaded_bitmap, offset_bit, nbits);
+    bitmap_set(r->uploaded_bitmap, start_bit, nbits);
 }
 
 static void update_memory_buffer(NV2AState *d, hwaddr addr, hwaddr size)