diff --git a/src/emu/machine/z8536.c b/src/emu/machine/z8536.c
index 34b9a935b4e..fc2967f6800 100644
--- a/src/emu/machine/z8536.c
+++ b/src/emu/machine/z8536.c
@@ -885,7 +885,7 @@ inline bool z8536_device::counter_gated(device_timer_id id)
 inline void z8536_device::count(device_timer_id id)
 {
 	if (!counter_gated(id)) return;
-	if (!m_register[COUNTER_TIMER_1_COMMAND_AND_STATUS + id] & CTCS_CIP) return;
+	if (!(m_register[COUNTER_TIMER_1_COMMAND_AND_STATUS + id] & CTCS_CIP)) return;
 
 	// count down
 	m_counter[id]--;
diff --git a/src/lib/util/coreutil.c b/src/lib/util/coreutil.c
index d096375be44..ecbbbd0249c 100644
--- a/src/lib/util/coreutil.c
+++ b/src/lib/util/coreutil.c
@@ -91,7 +91,7 @@ UINT32 bcd_2_dec(UINT32 a)
 
 int gregorian_is_leap_year(int year)
 {
-	return !(year % 100 ? year % 4 : year % 400);
+	return !((year % 100) ? (year % 4) : (year % 400));
 }
 
 
diff --git a/src/mame/drivers/multfish.c b/src/mame/drivers/multfish.c
index b0a9d8a03b3..ae3aad06269 100644
--- a/src/mame/drivers/multfish.c
+++ b/src/mame/drivers/multfish.c
@@ -435,10 +435,10 @@ WRITE8_MEMBER(multfish_state::rollfr_hopper_w)
 
 
 	m_hopper_motor = data & 0x10;
-        coin_lockout_w(machine(), 0, !data & 0x01);
-        coin_lockout_w(machine(), 1, !data & 0x01);
-        coin_lockout_w(machine(), 2, !data & 0x01);
-        coin_lockout_w(machine(), 3, !data & 0x01);
+        coin_lockout_w(machine(), 0,~data & 0x01);
+        coin_lockout_w(machine(), 1,~data & 0x01);
+        coin_lockout_w(machine(), 2,~data & 0x01);
+        coin_lockout_w(machine(), 3,~data & 0x01);
         coin_lockout_w(machine(), 4, data & 0x04);
         coin_lockout_w(machine(), 5, data & 0x04);
         coin_lockout_w(machine(), 6, data & 0x04);
diff --git a/src/mame/drivers/peplus.c b/src/mame/drivers/peplus.c
index 802e955b859..7c911c763b3 100644
--- a/src/mame/drivers/peplus.c
+++ b/src/mame/drivers/peplus.c
@@ -621,7 +621,7 @@ READ8_MEMBER(peplus_state::peplus_input_bank_a_r)
 
 	if (curr_cycles - m_last_door > door_wait) {
 		if ((ioport("DOOR")->read_safe(0xff) & 0x01) == 0x01) {
-			m_door_open = (!m_door_open & 0x01);
+			m_door_open = (m_door_open ^ 0x01) & 0x01;
 		} else {
 			m_door_open = 1;
 		}
diff --git a/src/mame/video/goldstar.c b/src/mame/video/goldstar.c
index 540d665b4b1..62b8535fdbe 100644
--- a/src/mame/video/goldstar.c
+++ b/src/mame/video/goldstar.c
@@ -383,7 +383,7 @@ SCREEN_UPDATE_IND16( goldstar )
 
 	bitmap.fill(get_black_pen(screen.machine()), cliprect);
 
-	if (!state->m_cm_enable_reg &0x01)
+	if (!(state->m_cm_enable_reg &0x01))
 		return 0;
 
 	if (state->m_cm_enable_reg &0x08)
@@ -434,7 +434,7 @@ SCREEN_UPDATE_IND16( bingowng )
 
 	bitmap.fill(get_black_pen(screen.machine()), cliprect);
 
-	if (!state->m_cm_enable_reg &0x01)
+	if (!(state->m_cm_enable_reg &0x01))
 		return 0;
 
 	if (state->m_cm_enable_reg &0x08)
@@ -477,7 +477,7 @@ SCREEN_UPDATE_IND16( magical )
 
 	bitmap.fill(get_black_pen(screen.machine()), cliprect);
 
-	if (!state->m_cm_enable_reg &0x01)
+	if (!(state->m_cm_enable_reg &0x01))
 		return 0;
 
 	if (state->m_cm_enable_reg &0x08)
@@ -536,7 +536,7 @@ SCREEN_UPDATE_IND16( unkch )
 
 	bitmap.fill(get_black_pen(screen.machine()), cliprect);
 
-	if (!state->m_cm_enable_reg &0x01)
+	if (!(state->m_cm_enable_reg &0x01))
 		return 0;
 
 	if (state->m_cm_enable_reg &0x08)
@@ -590,7 +590,7 @@ SCREEN_UPDATE_IND16( cmast91 )
 
 	bitmap.fill(get_black_pen(screen.machine()), cliprect);
 
-	if (!state->m_cm_enable_reg &0x01)
+	if (!(state->m_cm_enable_reg &0x01))
 		return 0;
 
 	if (state->m_cm_enable_reg &0x08)
@@ -626,7 +626,7 @@ SCREEN_UPDATE_IND16( amcoe1a )
 
 	bitmap.fill(get_black_pen(screen.machine()), cliprect);
 
-	if (!state->m_cm_enable_reg &0x01)
+	if (!(state->m_cm_enable_reg &0x01))
 		return 0;
 
 	if (state->m_cm_enable_reg &0x08)