diff --git a/src/port_6x.c b/src/port_6x.c
index 750b9678c..971b92d28 100644
--- a/src/port_6x.c
+++ b/src/port_6x.c
@@ -46,6 +46,8 @@
 #define PORT_6X_MIRROR   4
 #define PORT_6X_SWA      8
 
+static int cycles_sub = 0;
+
 static void
 port_6x_write(uint16_t port, uint8_t val, void *priv)
 {
@@ -53,7 +55,7 @@ port_6x_write(uint16_t port, uint8_t val, void *priv)
 
     port &= 3;
 
-    cycles -= ISA_CYCLES(8);
+    cycles -= cycles_sub;
 
     if ((port == 3) && (dev->flags & PORT_6X_MIRROR))
         port = 1;
@@ -83,7 +85,7 @@ port_61_read_simple(UNUSED(uint16_t port), UNUSED(void *priv))
 {
     uint8_t ret = ppi.pb & 0x1f;
 
-    cycles -= ISA_CYCLES(8);
+    cycles -= cycles_sub;
 
     if (ppispeakon)
         ret |= 0x20;
@@ -97,7 +99,7 @@ port_61_read(UNUSED(uint16_t port), void *priv)
     const port_6x_t *dev = (port_6x_t *) priv;
     uint8_t          ret = 0xff;
 
-    cycles -= ISA_CYCLES(8);
+    cycles -= cycles_sub;
 
     if (dev->flags & PORT_6X_EXT_REF) {
         ret = ppi.pb & 0x0f;
@@ -197,6 +199,8 @@ port_6x_init(const device_t *info)
     if (dev->flags & PORT_6X_SWA)
         io_sethandler(0x0062, 1, port_62_read, NULL, NULL, NULL, NULL, NULL, dev);
 
+    cycles_sub = is486 ? ISA_CYCLES(8) : 0;
+
     return dev;
 }