diff --git a/Machines/MasterSystem/MasterSystem.cpp b/Machines/MasterSystem/MasterSystem.cpp
index a70ff06d8..c6cfcc518 100644
--- a/Machines/MasterSystem/MasterSystem.cpp
+++ b/Machines/MasterSystem/MasterSystem.cpp
@@ -117,7 +117,9 @@ class ConcreteMachine:
 			map(write_pointers_, nullptr, 0x10000, 0);
 
 			// Take a copy of the cartridge and place it into memory.
-			cartridge_ = target.media.cartridges[0]->get_segments()[0].data;
+			if(!target.media.cartridges.empty()) {
+				cartridge_ = target.media.cartridges[0]->get_segments()[0].data;
+			}
 			if(cartridge_.size() < 48*1024) {
 				std::size_t new_space = 48*1024 - cartridge_.size();
 				cartridge_.resize(48*1024);
@@ -138,7 +140,15 @@ class ConcreteMachine:
 				//
 				//	0072ed54 = US/European BIOS 1.3
 				//	48d44a13 = Japanese BIOS 2.1
-				const auto roms = rom_fetcher({ {"MasterSystem", "the Master System BIOS", "bios.sms", 8*1024, { 0x0072ed54, 0x48d44a13 } } });
+				const bool is_japanese = target.region == Target::Region::Japan;
+				const auto roms = rom_fetcher(
+					{ {"MasterSystem",
+						is_japanese ? "the Japanese Master System BIOS" : "the European/US Master System BIOS",
+						is_japanese ? "japanese-bios.sms" : "bios.sms",
+						8*1024,
+						{ is_japanese ? 0x48d44a13u : 0x0072ed54u }
+					} }
+				);
 				if(!roms[0]) {
 					// No BIOS found; attempt to boot as though it has already disabled itself.
 					memory_control_ |= 0x08;
@@ -160,6 +170,7 @@ class ConcreteMachine:
 			}
 
 			// Apply a relatively low low-pass filter. More guidance needed here.
+			// TODO: this is disabled for now since it isn't applicable for the FM chip, I think.
 //			speaker_.set_high_frequency_cutoff(8000);
 
 			// Set default mixer levels: FM off, SN full-throttle.
diff --git a/ROMImages/MasterSystem/readme.txt b/ROMImages/MasterSystem/readme.txt
index ed5073cc9..823c3bcb7 100644
--- a/ROMImages/MasterSystem/readme.txt
+++ b/ROMImages/MasterSystem/readme.txt
@@ -2,4 +2,7 @@ BIOS files would ordinarily go here; the copyright status of these is uncertain
 
 Expected files:
 
-bios.sms — the EU/US Master System BIOS.
\ No newline at end of file
+bios.sms — the EU/US Master System BIOS.
+japanese-bios.sms — the Japanese Master System BIOS.
+
+If the file sought by the emulator is missing, it will attempt to boot a game without using the BIOS.
\ No newline at end of file