diff --git a/python/swiftest/swiftest/init_cond.py b/python/swiftest/swiftest/init_cond.py
index 395ebdb89..83ced66b8 100644
--- a/python/swiftest/swiftest/init_cond.py
+++ b/python/swiftest/swiftest/init_cond.py
@@ -263,7 +263,7 @@ def solar_system_horizons(plname, idval, param, ephemerides_start_date, ds):
         pvec = np.vstack([pvec, p7, p8, p9, p10, p11, p12])
 
         if idval is None:
-            plid = np.array([planetid[key]+1], dtype=int)
+            plid = np.array([planetid[key]], dtype=int) + 1
         else:
             plid = np.array([idval]+1, dtype=int)