diff --git a/mednafen/psx/frontio.cpp b/mednafen/psx/frontio.cpp
index a35b022f..02e7ce0b 100644
--- a/mednafen/psx/frontio.cpp
+++ b/mednafen/psx/frontio.cpp
@@ -783,6 +783,10 @@ int32_t FrontIO::Update(int32_t timestamp)
                   ReceiveInProgress = false;
                   ReceiveBufferAvail = true;
 
+                  /* PSXRecomp oracle hook: byte exchange complete. */
+                  if(MDFN_UNLIKELY(sio_trace_cb))
+                     sio_trace_cb(TransmitBuffer, ReceiveBuffer, (uint16_t)Control);
+
                   if(Control & 0x800)
                   {
                      istatus = true;
diff --git a/mednafen/psx/frontio.h b/mednafen/psx/frontio.h
index 8a67f5af..d9a260ca 100644
--- a/mednafen/psx/frontio.h
+++ b/mednafen/psx/frontio.h
@@ -95,8 +95,15 @@ class FrontIO
 
       int StateAction(StateMem* sm, int load, int data_only);
 
+      /* PSXRecomp oracle hook: fires once per completed SIO byte exchange
+       * (tx byte sent, rx byte received, current Control register). */
+      typedef void (*sio_trace_cb_t)(uint8_t tx, uint8_t rx, uint16_t ctrl);
+      void SetSIOTraceCallback(sio_trace_cb_t cb) { sio_trace_cb = cb; }
+
    private:
 
+      sio_trace_cb_t sio_trace_cb = nullptr;
+
       void DoDSRIRQ(void);
       void CheckStartStopPending(int32_t timestamp, bool skip_event_set = false);