diff --git a/src/portable/raspberrypi/rp2040/rp2040_usb.c b/src/portable/raspberrypi/rp2040/rp2040_usb.c
index 5c536e31..a6e0ed56 100644
--- a/src/portable/raspberrypi/rp2040/rp2040_usb.c
+++ b/src/portable/raspberrypi/rp2040/rp2040_usb.c
@@ -154,7 +154,14 @@ void _hw_endpoint_xfer_start(struct hw_endpoint *ep, uint8_t *buffer, uint16_t t
     ep->total_len = total_len;
     ep->len = 0;
     // FIXME: What if low speed
-    ep->transfer_size = total_len > 64 ? 64 : total_len;
+    if(ep->transfer_type == TUSB_XFER_ISOCHRONOUS)
+    {
+        ep->transfer_size = tu_min32(total_len, ep->wMaxPacketSize);
+    }
+    else
+    {
+        ep->transfer_size = tu_min32(total_len, 64);
+    }
     ep->active = true;
     ep->user_buf = buffer;
     // Recalculate if this is the last buffer
@@ -232,7 +239,15 @@ bool _hw_endpoint_xfer_continue(struct hw_endpoint *ep)
 
     // Now we have synced our state with the hardware. Is there more data to transfer?
     uint remaining_bytes = ep->total_len - ep->len;
-    ep->transfer_size = remaining_bytes > 64 ? 64 : remaining_bytes;
+
+    if(ep->transfer_type == TUSB_XFER_ISOCHRONOUS)
+    {
+        ep->transfer_size = tu_min32(remaining_bytes,ep->wMaxPacketSize);
+    }
+    else
+    {
+        ep->transfer_size = tu_min32(remaining_bytes, 64);
+    }
     _hw_endpoint_update_last_buf(ep);
 
     // Can happen because of programmer error so check for it