diff --git a/src/devices/cpu/tms9900/tms9995.h b/src/devices/cpu/tms9900/tms9995.h
index dd9d914e985..76e0ab7ec1c 100644
--- a/src/devices/cpu/tms9900/tms9995.h
+++ b/src/devices/cpu/tms9900/tms9995.h
@@ -55,6 +55,7 @@ public:
 
 	// For debugger access
 	uint8_t debug_read_onchip_memory(offs_t addr) { return m_onchip_memory[addr & 0xff]; };
+	void debug_write_onchip_memory(offs_t addr, uint8_t data) { m_onchip_memory[addr & 0xff] = data; };
 	bool is_onchip(offs_t addrb) { return (((addrb & 0xff00)==0xf000 && (addrb < 0xf0fc)) || ((addrb & 0xfffc)==0xfffc)) && !m_mp9537; }
 
 	void set_overflow_interrupt( int enable ) { m_check_overflow = (enable!=0); }
diff --git a/src/mame/drivers/geneve.cpp b/src/mame/drivers/geneve.cpp
index f86282a5847..76d36356209 100644
--- a/src/mame/drivers/geneve.cpp
+++ b/src/mame/drivers/geneve.cpp
@@ -632,16 +632,15 @@ void geneve_state::memwrite(offs_t offset, uint8_t data)
 
 	if (machine().side_effects_disabled())
 	{
-		// TODO: add method to tms9995
-//      if (m_cpu->is_onchip(offset))
-//      {
-//          m_cpu->debug_write_onchip_memory(offset, data);
-//          return;
-//      }
+		if (m_cpu->is_onchip(offset))
+		{
+			m_cpu->debug_write_onchip_memory(offset, data);
+			return;
+		}
 
 		// The debugger does not call setaddress, so we do it here
 		// Also, the decode result is replaced by the debugger version
-		setaddress_debug(true, addr13, 0);
+		setaddress_debug(true, offset, 0);
 	}
 
 	// Video write (never by debugger)