diff --git a/src/devices/bus/isa/isa.h b/src/devices/bus/isa/isa.h
index 2eddae32015..4ba5b764d24 100644
--- a/src/devices/bus/isa/isa.h
+++ b/src/devices/bus/isa/isa.h
@@ -215,7 +215,11 @@ public:
 	}
 
 	void install_device(offs_t start, offs_t end, read8_delegate rhandler, write8_delegate whandler);
-	template<typename T> void install_device(offs_t addrstart, offs_t addrend, T &device, void (T::*map)(class address_map &map), int bits = 8, uint64_t unitmask = 0xffffffffffffffffU)
+	template<typename T> void install_device(offs_t addrstart, offs_t addrend, T &device, void (T::*map)(class address_map &map), int bits = 8)
+	{
+		m_iospace->install_device(addrstart, addrend, device, map, bits, 0xffffffffffffffffU >> (64 - m_iospace->data_width()));
+	}
+	template<typename T> void install_device(offs_t addrstart, offs_t addrend, T &device, void (T::*map)(class address_map &map), int bits, uint64_t unitmask)
 	{
 		m_iospace->install_device(addrstart, addrend, device, map, bits, unitmask);
 	}
diff --git a/src/emu/screen.cpp b/src/emu/screen.cpp
index ea523836ba0..8b4bcfa0cff 100644
--- a/src/emu/screen.cpp
+++ b/src/emu/screen.cpp
@@ -1235,9 +1235,12 @@ void screen_device::update_now()
 		// if the line before us was incomplete, we must do it in two pieces
 		if (m_partial_scan_hpos > 0)
 		{
-			s32 save_scan = m_partial_scan_hpos;
-			update_partial(current_vpos - 2);
-			m_partial_scan_hpos = save_scan;
+			if (current_vpos > 1)
+			{
+				s32 save_scan = m_partial_scan_hpos;
+				update_partial(current_vpos - 2);
+				m_partial_scan_hpos = save_scan;
+			}
 
 			// now finish the previous partial scanline
 			int scanline = current_vpos - 1;