diff --git a/src/portable/st/synopsys/dcd_synopsys.c b/src/portable/st/synopsys/dcd_synopsys.c
index ca306ff8f..9aeec79e6 100644
--- a/src/portable/st/synopsys/dcd_synopsys.c
+++ b/src/portable/st/synopsys/dcd_synopsys.c
@@ -416,7 +416,7 @@ void dcd_init (uint8_t rhport)
   if ( rhport == 1 )
   {
     // On selected MCUs HS port1 can be used with external PHY via ULPI interface
-
+#if CFG_TUSB_RHPORT1_MODE & OPT_MODE_HIGH_SPEED
     // deactivate internal PHY
     usb_otg->GCCFG &= ~USB_OTG_GCCFG_PWRDWN;
 
@@ -425,6 +425,9 @@ void dcd_init (uint8_t rhport)
 
     // Select default internal VBUS Indicator and Drive for ULPI
     usb_otg->GUSBCFG &= ~(USB_OTG_GUSBCFG_ULPIEVBUSD | USB_OTG_GUSBCFG_ULPIEVBUSI);
+#else
+    usb_otg->GUSBCFG |= USB_OTG_GUSBCFG_PHYSEL;
+#endif
 
 #if defined(USB_HS_PHYC)
     // Highspeed with embedded UTMI PHYC
@@ -467,8 +470,8 @@ void dcd_init (uint8_t rhport)
 
   set_speed(rhport, TUD_OPT_HIGH_SPEED ? TUSB_SPEED_HIGH : TUSB_SPEED_FULL);
 
-  // Enable internal USB transceiver.
-  if ( rhport == 0 ) usb_otg->GCCFG |= USB_OTG_GCCFG_PWRDWN;
+  // Enable internal USB transceiver, unless using HS core (port 1) with external PHY.
+  if (!(rhport == 1 && (CFG_TUSB_RHPORT1_MODE & OPT_MODE_HIGH_SPEED))) usb_otg->GCCFG |= USB_OTG_GCCFG_PWRDWN;
 
   usb_otg->GINTMSK |= USB_OTG_GINTMSK_USBRST   | USB_OTG_GINTMSK_ENUMDNEM |
       USB_OTG_GINTMSK_USBSUSPM | USB_OTG_GINTMSK_WUIM     |