diff --git a/src/mame/apple/apple2gs.cpp b/src/mame/apple/apple2gs.cpp
index 0ab1d16e5f8bf..44f7e2d500c1d 100644
--- a/src/mame/apple/apple2gs.cpp
+++ b/src/mame/apple/apple2gs.cpp
@@ -93,7 +93,8 @@ namespace {
 #define A2GS_MASTER_CLOCK (XTAL(28'636'363))
 #define A2GS_14M    (A2GS_MASTER_CLOCK/2)
 #define A2GS_7M     (A2GS_MASTER_CLOCK/4)
-#define A2GS_1M     (A2GS_MASTER_CLOCK/28)
+#define A2GS_2_8M   (A2GS_MASTER_CLOCK/10)
+#define A2GS_1M     (XTAL(1021800))
 
 #define A2GS_UPPERBANK_TAG "inhbank"
 #define A2GS_AUXUPPER_TAG "inhaux"
@@ -519,7 +520,7 @@ class apple2gs_state : public driver_device
 		}
 		else
 		{
-			m_maincpu->set_unscaled_clock(1021800);
+			m_maincpu->set_unscaled_clock(A2GS_1M);
 		}
 	}
 
@@ -539,11 +540,11 @@ class apple2gs_state : public driver_device
 
 		if (isfast)
 		{
-			m_maincpu->set_unscaled_clock(A2GS_14M/5);
+			m_maincpu->set_unscaled_clock(A2GS_2_8M);
 		}
 		else
 		{
-			m_maincpu->set_unscaled_clock(1021800);
+			m_maincpu->set_unscaled_clock(A2GS_1M);
 		}
 	}
 
@@ -847,7 +848,7 @@ void apple2gs_state::machine_reset()
 	m_slow_counter = 0;
 
 	// always assert full speed on reset
-	m_maincpu->set_unscaled_clock(A2GS_14M/5);
+	m_maincpu->set_unscaled_clock(A2GS_2_8M);
 	m_last_speed = true;
 
 	m_sndglu_ctrl = 0;
@@ -971,7 +972,7 @@ void apple2gs_state::update_speed()
 		}
 		else
 		{
-			m_maincpu->set_unscaled_clock(isfast ? A2GS_14M / 5 : A2GS_1M);
+			m_maincpu->set_unscaled_clock(isfast ? A2GS_2_8M : A2GS_1M);
 		}
 		m_last_speed = isfast;
 	}
@@ -3743,7 +3744,7 @@ INPUT_PORTS_END
 void apple2gs_state::apple2gs(machine_config &config)
 {
 	/* basic machine hardware */
-	G65816(config, m_maincpu, A2GS_MASTER_CLOCK/10);
+	G65816(config, m_maincpu, A2GS_2_8M);
 	m_maincpu->set_addrmap(AS_PROGRAM, &apple2gs_state::apple2gs_map);
 	m_maincpu->set_addrmap(g65816_device::AS_VECTORS, &apple2gs_state::vectors_map);
 	m_maincpu->set_dasm_override(FUNC(apple2gs_state::dasm_trampoline));
@@ -3811,7 +3812,7 @@ void apple2gs_state::apple2gs(machine_config &config)
 	ADDRESS_MAP_BANK(config, A2GS_C300_TAG).set_map(&apple2gs_state::c300bank_map).set_options(ENDIANNESS_LITTLE, 8, 32, 0x100);
 
 	/* serial */
-	SCC85C30(config, m_scc, A2GS_14M / 2);
+	SCC85C30(config, m_scc, A2GS_7M);
 	m_scc->configure_channels(3'686'400, 3'686'400, 3'686'400, 3'686'400);
 	m_scc->out_int_callback().set(FUNC(apple2gs_state::scc_irq_w));
 	m_scc->out_txda_callback().set("printer", FUNC(rs232_port_device::write_txd));
@@ -3842,7 +3843,7 @@ void apple2gs_state::apple2gs(machine_config &config)
 	A2BUS_SLOT(config, "sl6", A2GS_7M, m_a2bus, apple2gs_cards, nullptr);
 	A2BUS_SLOT(config, "sl7", A2GS_7M, m_a2bus, apple2gs_cards, nullptr);
 
-	IWM(config, m_iwm, A2GS_7M, A2GS_MASTER_CLOCK/14);
+	IWM(config, m_iwm, A2GS_7M, A2GS_1M*2);
 	m_iwm->phases_cb().set(FUNC(apple2gs_state::phases_w));
 	m_iwm->sel35_cb().set(FUNC(apple2gs_state::sel35_w));
 	m_iwm->devsel_cb().set(FUNC(apple2gs_state::devsel_w));