diff --git a/src/emu/sound/dac.h b/src/emu/sound/dac.h
index 23e31e308e7..0beb199e174 100644
--- a/src/emu/sound/dac.h
+++ b/src/emu/sound/dac.h
@@ -3,10 +3,10 @@
 #ifndef __DAC_H__
 #define __DAC_H__
 
-void dac_data_w(const device_config *device, UINT8 data);
-void dac_signed_data_w(const device_config *device, UINT8 data);
-void dac_data_16_w(const device_config *device, UINT16 data);
-void dac_signed_data_16_w(const device_config *device, UINT16 data);
+void dac_data_w(const device_config *device, UINT8 data) ATTR_NONNULL;
+void dac_signed_data_w(const device_config *device, UINT8 data) ATTR_NONNULL;
+void dac_data_16_w(const device_config *device, UINT16 data) ATTR_NONNULL;
+void dac_signed_data_16_w(const device_config *device, UINT16 data) ATTR_NONNULL;
 
 WRITE8_DEVICE_HANDLER( dac_w );
 WRITE8_DEVICE_HANDLER( dac_signed_w );