diff --git a/src/devices/video/snes_ppu.cpp b/src/devices/video/snes_ppu.cpp
index 2142b59681f..43fbeeac74f 100644
--- a/src/devices/video/snes_ppu.cpp
+++ b/src/devices/video/snes_ppu.cpp
@@ -808,10 +808,11 @@ inline void snes_ppu_device::update_line( uint16_t curline, uint8_t layer_idx, u
 
 	uint32_t y = layer.mosaic_enabled ? layer.mosaic_offset : curline;
 
+	//printf("h:%d i:%d l:%d ", hires ? 1 : 0, m_interlace, curline);
 	if (hires)
 	{
 		hscroll <<= 1;
-		if (m_interlace == 2) y = y << 1 | (m_stat78 >> 7);
+		if (m_interlace == 2) y = (y & ~1) | (m_stat78 >> 7);
 	}
 
 	uint32_t mosaic_counter = 1;