diff --git a/Machines/MSX/Cartridges/KonamiWithSCC.hpp b/Machines/MSX/Cartridges/KonamiWithSCC.hpp
index 00bb7141e..7f1e8dc16 100644
--- a/Machines/MSX/Cartridges/KonamiWithSCC.hpp
+++ b/Machines/MSX/Cartridges/KonamiWithSCC.hpp
@@ -43,7 +43,7 @@ class KonamiWithSCCROMSlotHandler: public MemorySlotHandler {
 					}
 					if((value&0x3f) == 0x3f) {
 						scc_is_visible_ = true;
-						slot_.unmap(0x8000, 0x2000);
+						slot_.map_handler(0x8000, 0x2000);
 					} else {
 						scc_is_visible_ = false;
 						slot_.map(value * 0x2000, 0x8000, 0x2000);
diff --git a/Machines/MSX/MSX.cpp b/Machines/MSX/MSX.cpp
index fd5b9e972..52af973ef 100644
--- a/Machines/MSX/MSX.cpp
+++ b/Machines/MSX/MSX.cpp
@@ -291,7 +291,7 @@ class ConcreteMachine:
 				disk_slot().set_source(dos);
 
 				disk_slot().map(0, 0x4000, 0x2000);
-				disk_slot().unmap(0x6000, 0x2000);
+				disk_slot().map_handler(0x6000, 0x2000);
 			}
 
 			// Insert the media.
diff --git a/Machines/MSX/MemorySlotHandler.cpp b/Machines/MSX/MemorySlotHandler.cpp
index 7fb280603..79d4c69e3 100644
--- a/Machines/MSX/MemorySlotHandler.cpp
+++ b/Machines/MSX/MemorySlotHandler.cpp
@@ -16,10 +16,7 @@ PrimarySlot::PrimarySlot(MemorySlotChangeHandler &handler) :
 	subslots_{handler, handler, handler, handler} {}
 
 MemorySlot::MemorySlot(MemorySlotChangeHandler &handler) : handler_(handler) {
-	for(int region = 0; region < 8; region++) {
-		read_pointers_[region] = unmapped.data();
-		write_pointers_[region] = scratch.data();
-	}
+	unmap(0x0000, 0x10000);
 }
 
 void PrimarySlot::set_secondary_paging(uint8_t value) {
@@ -85,7 +82,7 @@ void MemorySlot::map(std::size_t source_address, uint16_t destination_address, s
 	handler_.did_page();
 }
 
-void MemorySlot::unmap(uint16_t destination_address, std::size_t length) {
+void MemorySlot::map_handler(uint16_t destination_address, std::size_t length) {
 	assert(!(destination_address & 8191));
 	assert(!(length & 8191));
 	assert(size_t(destination_address) + length <= 65536);
@@ -97,6 +94,19 @@ void MemorySlot::unmap(uint16_t destination_address, std::size_t length) {
 	handler_.did_page();
 }
 
+void MemorySlot::unmap(uint16_t destination_address, std::size_t length) {
+	assert(!(destination_address & 8191));
+	assert(!(length & 8191));
+	assert(size_t(destination_address) + length <= 65536);
+
+	for(std::size_t c = 0; c < (length >> 13); ++c) {
+		read_pointers_[(destination_address >> 13) + c] = unmapped.data();
+		write_pointers_[(destination_address >> 13) + c] = scratch.data();
+	}
+
+	handler_.did_page();
+}
+
 MemorySlot &PrimarySlot::subslot(int slot) {
 	return subslots_[slot];
 }
diff --git a/Machines/MSX/MemorySlotHandler.hpp b/Machines/MSX/MemorySlotHandler.hpp
index 874b76b4f..49f58ab09 100644
--- a/Machines/MSX/MemorySlotHandler.hpp
+++ b/Machines/MSX/MemorySlotHandler.hpp
@@ -69,9 +69,13 @@ class MemorySlot {
 			std::size_t length);
 
 		/// Marks the region indicated by @c destination_address and @c length
-		/// as unmapped. In practical terms that means that a @c MemorySlotHandler
-		/// will be used to field accesses to that area, allowing for areas that are not
-		/// backed by memory to be modelled.
+		/// as requiring calls into this slot's MemorySlotHandler.
+		void map_handler(
+			uint16_t destination_address,
+			std::size_t length);
+
+		/// Marks the region indicated by @c destination_address and @c length
+		/// as unoccupied.
 		void unmap(
 			uint16_t destination_address,
 			std::size_t length);