diff --git a/src/d3d9/d3d9_device.cpp b/src/d3d9/d3d9_device.cpp
index 7419cc483..64633b833 100644
--- a/src/d3d9/d3d9_device.cpp
+++ b/src/d3d9/d3d9_device.cpp
@@ -4175,6 +4175,10 @@ namespace dxvk {
     if (desc.Pool != D3DPOOL_DEFAULT)
       Flags &= ~(D3DLOCK_DISCARD | D3DLOCK_NOOVERWRITE);
 
+    // Ignore DISCARD if we are doing a partial lock.
+    if (OffsetToLock != 0 || (SizeToLock != 0 && SizeToLock != desc.Size))
+      Flags &= ~D3DLOCK_DISCARD;
+
     // Ignore READONLY if we are a WRITEONLY resource.
     if (desc.Usage & D3DUSAGE_WRITEONLY)
       Flags &= ~D3DLOCK_READONLY;