diff --git a/monetio/sat/_tropomi_l2_no2_mm.py b/monetio/sat/_tropomi_l2_no2_mm.py
index a575893f..66ced287 100644
--- a/monetio/sat/_tropomi_l2_no2_mm.py
+++ b/monetio/sat/_tropomi_l2_no2_mm.py
@@ -103,7 +103,7 @@ def get_extra(varname_, *, dct_=None, default_group="PRODUCT"):
             # Tropopause pressure
             ptrop = xr.full_like(itrop, np.nan, dtype=ds["preslev"].dtype)
             for i in np.unique(itrop):
-                if np.isnan(i):
+                if np.isnan(i) or i < 0 or i >= p.sizes["z"]:
                     continue
                 ptrop = xr.where(itrop == i, p.isel(z=int(i)), ptrop)
             ds["troppres"] = ptrop