diff --git a/src/mess/machine/isa_sblaster.h b/src/mess/machine/isa_sblaster.h
index efe9f86f5f1..e110a5c2258 100644
--- a/src/mess/machine/isa_sblaster.h
+++ b/src/mess/machine/isa_sblaster.h
@@ -162,7 +162,7 @@ protected:
 		virtual void dack16_w(int line, UINT16 data);
 		virtual void drq16_w(int state) { m_isa->drq5_w(state); }
 		virtual void drq_w(int state) { m_isa->drq1_w(state); }
-		virtual void irq_w(int state, int source) { (state?m_dsp.irq_active|=source:m_dsp.irq_active&=~source); m_isa->irq5_w(m_dsp.irq_active&&1);  }
+		virtual void irq_w(int state, int source) { (state?m_dsp.irq_active|=source:m_dsp.irq_active&=~source); m_isa->irq5_w(m_dsp.irq_active);  }
 private:
 		UINT8 m_mpu_queue[16];
 		UINT8 m_tail;