diff --git a/CHANGES b/CHANGES
index bc87a732b..2b923ba6a 100644
--- a/CHANGES
+++ b/CHANGES
@@ -65,6 +65,7 @@ Other fixes:
  - FFmpeg: Fix some small memory leaks
  - FFmpeg: Fix encoding of time base
  - GB Core: Fix extracting SRAM when none is present
+ - GBA: Fix leak if attempting to load BIOS multiple times
  - GBA Savedata: Fix extracting save when not yet configured in-game
  - Qt: Force OpenGL paint engine creation thread (fixes mgba.io/i/1642)
  - Qt: Fix static compilation in MinGW (fixes mgba.io/i/1769)
diff --git a/src/gba/gba.c b/src/gba/gba.c
index f4ac50fe9..84ad8007e 100644
--- a/src/gba/gba.c
+++ b/src/gba/gba.c
@@ -443,7 +443,6 @@ void GBAYankROM(struct GBA* gba) {
 }
 
 void GBALoadBIOS(struct GBA* gba, struct VFile* vf) {
-	gba->biosVf = vf;
 	if (vf->size(vf) != SIZE_BIOS) {
 		mLOG(GBA, WARN, "Incorrect BIOS size");
 		return;
@@ -453,6 +452,11 @@ void GBALoadBIOS(struct GBA* gba, struct VFile* vf) {
 		mLOG(GBA, WARN, "Couldn't map BIOS");
 		return;
 	}
+	if (gba->biosVf) {
+		gba->biosVf->unmap(gba->biosVf, gba->memory.bios, SIZE_BIOS);
+		gba->biosVf->close(gba->biosVf);
+	}
+	gba->biosVf = vf;
 	gba->memory.bios = bios;
 	gba->memory.fullBios = 1;
 	uint32_t checksum = GBAChecksum(gba->memory.bios, SIZE_BIOS);
@@ -733,14 +737,14 @@ void GBAHitStub(struct ARMCore* cpu, uint32_t opcode) {
 
 void GBAIllegal(struct ARMCore* cpu, uint32_t opcode) {
 	struct GBA* gba = (struct GBA*) cpu->master;
+	if (cpu->executionMode == MODE_THUMB && (opcode & 0xFFC0) == 0xE800) {
+		mLOG(GBA, INFO, "Hit Wii U VC opcode: %08x", opcode);
+		return;
+	}
 	if (!gba->yankedRomSize) {
 		// TODO: More sensible category?
 		mLOG(GBA, WARN, "Illegal opcode: %08x", opcode);
 	}
-	if (cpu->executionMode == MODE_THUMB && (opcode & 0xFFC0) == 0xE800) {
-		mLOG(GBA, DEBUG, "Hit Wii U VC opcode: %08x", opcode);
-		return;
-	}
 #ifdef USE_DEBUGGERS
 	if (gba->debugger) {
 		struct mDebuggerEntryInfo info = {
diff --git a/src/platform/posix/memory.c b/src/platform/posix/memory.c
index 7892a5985..67cdd96d7 100644
--- a/src/platform/posix/memory.c
+++ b/src/platform/posix/memory.c
@@ -5,6 +5,17 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 #include <mgba-util/memory.h>
 
+#ifndef DISABLE_ANON_MMAP
+#ifdef __SANITIZE_ADDRESS__
+#define DISABLE_ANON_MMAP
+#elif defined(__has_feature)
+#if __has_feature(address_sanitizer)
+#define DISABLE_ANON_MMAP
+#endif
+#endif
+#endif
+
+#ifndef DISABLE_ANON_MMAP
 #include <sys/mman.h>
 
 void* anonymousMemoryMap(size_t size) {
@@ -14,3 +25,13 @@ void* anonymousMemoryMap(size_t size) {
 void mappedMemoryFree(void* memory, size_t size) {
 	munmap(memory, size);
 }
+#else
+void* anonymousMemoryMap(size_t size) {
+	return calloc(1, size);
+}
+
+void mappedMemoryFree(void* memory, size_t size) {
+	UNUSED(size);
+	free(memory);
+}
+#endif