diff --git a/backend/main.py b/backend/main.py
index 595bfa4..cd0b5c4 100644
--- a/backend/main.py
+++ b/backend/main.py
@@ -93,6 +93,7 @@ def register(req: RegisterRequest, db: Session = Depends(get_db)):
     email = req.email.strip().lower()
     if not email or not req.password:
         raise HTTPException(status_code=400, detail="Email and password are required")
+    pw_bytes_len = len(req.password.encode("utf-8"))
     _password_ok_or_400(req.password)
 
     try:
@@ -118,7 +119,10 @@ def register(req: RegisterRequest, db: Session = Depends(get_db)):
         raise HTTPException(status_code=500, detail=f"Database error: {str(e)}")
     except Exception as e:
         db.rollback()
-        raise HTTPException(status_code=500, detail=f"Internal error: {str(e)}")
+        raise HTTPException(
+            status_code=500,
+            detail=f"Internal error: {str(e)} (password_bytes_len={pw_bytes_len})",
+        )
 
 
 @app.post("/auth/login")