diff --git a/include/mgba/internal/gb/io.h b/include/mgba/internal/gb/io.h
index 665586e04..95afebe0f 100644
--- a/include/mgba/internal/gb/io.h
+++ b/include/mgba/internal/gb/io.h
@@ -102,8 +102,8 @@ enum GBIORegisters {
 	REG_UNK72 = 0x72,
 	REG_UNK73 = 0x73,
 	REG_UNK74 = 0x74,
-	REG_UNK75 = 0x75,
-	REG_UNK76 = 0x76,
+	REG_PCM12 = 0x75,
+	REG_PCM34 = 0x76,
 	REG_UNK77 = 0x77,
 	REG_MAX = 0x100
 };
diff --git a/src/gb/io.c b/src/gb/io.c
index bb20e44e9..254fb5232 100644
--- a/src/gb/io.c
+++ b/src/gb/io.c
@@ -101,7 +101,6 @@ static const uint8_t _registerMask[] = {
 	[REG_BCPS] = 0x40,
 	[REG_UNK6C] = 0xFE,
 	[REG_SVBK] = 0xF8,
-	[REG_UNK75] = 0x8F,
 	[REG_IE]   = 0xE0,
 };