diff --git a/src/gfx.h b/src/gfx.h
index 476f7420ac..11e9875f76 100644
--- a/src/gfx.h
+++ b/src/gfx.h
@@ -92,7 +92,7 @@ void gfx_draw_all_dirty_blocks();
 void gfx_redraw_screen_rect(short left, short top, short right, short bottom);
 void gfx_invalidate_screen();
 
-void gfx_draw_rain(int left, int top, int width, int height, uint32 x_start, uint32 y_start);
+void gfx_draw_rain(int left, int top, int width, int height, sint32 x_start, sint32 y_start);
 
 rct_drawpixelinfo* clip_drawpixelinfo(rct_drawpixelinfo* dpi, int left, int width, int top, int height);