diff --git a/src/emu/bus/isa/num9rev.c b/src/emu/bus/isa/num9rev.c
index b15258f4653..3fe6e7469f3 100644
--- a/src/emu/bus/isa/num9rev.c
+++ b/src/emu/bus/isa/num9rev.c
@@ -22,11 +22,11 @@ UPD7220_DISPLAY_PIXELS_MEMBER( isa8_number_9_rev_device::hgdc_display_pixels )
 	{
 		rgb_t color(0);
 		UINT16 overlay;
-		if(((address << 4) + 0xc0016) > (1024*1024))
+		if(((address << 3) + 0xc0016) > (1024*1024))
 			return;
 		for(int i = 0; i < 16; i++)
 		{
-			UINT32 addr = (address << 4) + i;
+			UINT32 addr = (address << 3) + i;
 			overlay = m_ram[addr + 0xc0000] << 1;
 			overlay = m_overlay[overlay + ((m_mode & 8) ? 512 : 0)] | (m_overlay[overlay + 1 + ((m_mode & 8) ? 512 : 0)] << 8);
 			color.set_r(pal->entry_color(m_ram[addr] | ((overlay & 0xf) << 8)).r());
@@ -37,7 +37,7 @@ UPD7220_DISPLAY_PIXELS_MEMBER( isa8_number_9_rev_device::hgdc_display_pixels )
 	}
 	else
 	{
-		if(((address << 4) + 16) > (1024*1024))
+		if(((address << 3) + 16) > (1024*1024))
 			return;
 		for(int i = 0; i < 16; i++)
 			bitmap.pix32(y, x + i) = pal->entry_color(m_ram[(address << 4) + i]);
diff --git a/src/mess/drivers/pc9801.c b/src/mess/drivers/pc9801.c
index ed1707554d1..e394c2ffbf1 100644
--- a/src/mess/drivers/pc9801.c
+++ b/src/mess/drivers/pc9801.c
@@ -1337,8 +1337,8 @@ inline UINT16 pc9801_state::egc_do_partial_op(int plane, UINT16 src, UINT16 pat,
 
 	if(m_egc.regs[6] & 0x1000)
 	{
-		src_off = 16 - (m_egc.regs[6] & 0xf);
-		dst_off = 16 - ((m_egc.regs[6] >> 4) & 0xf);
+		src_off = 15 - (m_egc.regs[6] & 0xf);
+		dst_off = 15 - ((m_egc.regs[6] >> 4) & 0xf);
 	}
 	else
 	{
@@ -1350,13 +1350,13 @@ inline UINT16 pc9801_state::egc_do_partial_op(int plane, UINT16 src, UINT16 pat,
 	{
 		src = src_tmp << (dst_off - src_off);
 		src |= m_egc.leftover[plane];
-		m_egc.leftover[plane] = src_tmp >> (16 - (dst_off - src_off));
+		m_egc.leftover[plane] = src_tmp >> (15 - (dst_off - src_off));
 	}
 	else
 	{
 		src = src_tmp >> (src_off - dst_off);
-		src |= m_egc.leftover[plane] >> dst_off;
-		m_egc.leftover[plane] = src_tmp << (16 - (src_off - dst_off));
+		src |= m_egc.leftover[plane];
+		m_egc.leftover[plane] = src_tmp << (15 - (src_off - dst_off));
 	}
 
 	for(int i = 7; i >= 0; i--)
@@ -1377,15 +1377,18 @@ void pc9801_state::egc_blit_w(UINT32 offset, UINT16 data, UINT16 mem_mask)
 	int dst_off = (m_egc.regs[6] >> 4) & 0xf;
 	offset &= 0x3fff;
 
-	// mask off the bits past the end of the blit
-	if(m_egc.count < 16)
-		mask &= dir ? ((1 << (m_egc.count + 1)) - 1) : ~((1 << (15 - m_egc.count)) - 1);
-
-	// mask off the bits before the start
-	if(m_egc.first)
+	if((((m_egc.regs[2] >> 11) & 3) == 1) || ((((m_egc.regs[2] >> 11) & 3) == 2) && !BIT(m_egc.regs[2], 10)))
 	{
-		m_egc.leftover[0] = m_egc.leftover[1] = m_egc.leftover[2] = m_egc.leftover[3] = 0;
-		mask &= dir ? ~((1 << (15 - dst_off)) - 1) : ((1 << (dst_off + 1)) - 1);
+		// mask off the bits past the end of the blit
+		if(m_egc.count < 16)
+			mask &= dir ? ((1 << (m_egc.count + 1)) - 1) : ~((1 << (16 - m_egc.count)) - 1);
+
+		// mask off the bits before the start
+		if(m_egc.first)
+		{
+			m_egc.leftover[0] = m_egc.leftover[1] = m_egc.leftover[2] = m_egc.leftover[3] = 0;
+			mask &= dir ? ~((1 << (16 - dst_off)) - 1) : ((1 << (dst_off + 1)) - 1);
+		}
 	}
 
 	for(int i = 0; i < 4; i++)