diff --git a/dlls/wined3d/wined3d_private.h b/dlls/wined3d/wined3d_private.h
index 2125366d469..c90a77dbd49 100644
--- a/dlls/wined3d/wined3d_private.h
+++ b/dlls/wined3d/wined3d_private.h
@@ -438,7 +438,7 @@ enum vertexprocessing_mode {
 #define WINED3D_CONST_NUM_UNUSED ~0U
 
 struct stb_const_desc {
-    char                    texunit;
+    unsigned char           texunit;
     UINT                    const_num;
 };