diff --git a/src/devices/bus/gameboy/mbc.cpp b/src/devices/bus/gameboy/mbc.cpp
index 5bcc83377f3..5f867933516 100644
--- a/src/devices/bus/gameboy/mbc.cpp
+++ b/src/devices/bus/gameboy/mbc.cpp
@@ -64,6 +64,7 @@ gb_rom_mbc2_device::gb_rom_mbc2_device(const machine_config &mconfig, const char
 
 gb_rom_mbc3_device::gb_rom_mbc3_device(const machine_config &mconfig, const char *tag, device_t *owner, uint32_t clock)
 	: gb_rom_mbc_device(mconfig, GB_ROM_MBC3, tag, owner, clock)
+	, m_rtc_ready(0)
 {
 }