diff --git a/src/scida/customs/arepo/dataset.py b/src/scida/customs/arepo/dataset.py
index cf58381d..67b26887 100644
--- a/src/scida/customs/arepo/dataset.py
+++ b/src/scida/customs/arepo/dataset.py
@@ -424,12 +424,19 @@ def add_catalogIDs(self) -> None:
                 continue  # can happen for empty containers
             gidx = pdata["uid"]
 
+            # we need to make other dask arrays delayed,
+            # map_block does not incorrectly infer output shape from these
+            halocelloffsets_dlyd = delayed(halocelloffsets[:, num])
+            grpfirstsub_dlyd = delayed(grpfirstsub)
+            grpnsubs_dlyd = delayed(grpnsubs)
+            subhalocellcounts_dlyd = delayed(subhalocellcounts[:, num])
+
             sidx = compute_localsubhaloindex(
                 gidx,
-                halocelloffsets[:, num],
-                grpfirstsub,
-                grpnsubs,
-                subhalocellcounts[:, num],
+                halocelloffsets_dlyd,
+                grpfirstsub_dlyd,
+                grpnsubs_dlyd,
+                subhalocellcounts_dlyd,
                 index_unbound=index_unbound,
             )
 
@@ -509,8 +516,9 @@ def map_group_operation(
         )
 
     def add_groupquantity_to_particles(self, name, parttype="PartType0"):
+        pdata = self.data[parttype]
         assert (
-            name not in self.data[parttype]
+            name not in pdata
         )  # we simply map the name from Group to Particle for now. Should work (?)
         glen = self.data["Group"]["GroupLenType"]
         da_halocelloffsets = da.concatenate(
@@ -522,12 +530,12 @@ def add_groupquantity_to_particles(self, name, parttype="PartType0"):
             )  # remove last entry to match shape
         halocelloffsets = da_halocelloffsets.compute()
 
-        gidx = self.data[parttype]["uid"]
+        gidx = pdata["uid"]
         num = int(parttype[-1])
         hquantity = compute_haloquantity(
             gidx, halocelloffsets[:, num], self.data["Group"][name]
         )
-        self.data[parttype][name] = hquantity
+        pdata[name] = hquantity
 
     def get_grouplengths(self, parttype="PartType0"):
         """Get the total number of particles of a given type in all halos."""
@@ -1025,7 +1033,7 @@ def get_local_shidx_daskwrap(
 ) -> np.ndarray:
     gidx_start = gidx[0]
     gidx_count = gidx.shape[0]
-    return get_localshidx(
+    res = get_localshidx(
         gidx_start,
         gidx_count,
         halocelloffsets,
@@ -1034,12 +1042,13 @@ def get_local_shidx_daskwrap(
         shcellcounts,
         index_unbound=index_unbound,
     )
+    return res
 
 
 def compute_localsubhaloindex(
     gidx, halocelloffsets, shnumber, shcounts, shcellcounts, index_unbound=None
 ) -> da.Array:
-    return da.map_blocks(
+    res = da.map_blocks(
         get_local_shidx_daskwrap,
         gidx,
         halocelloffsets,
@@ -1049,6 +1058,7 @@ def compute_localsubhaloindex(
         index_unbound=index_unbound,
         meta=np.array((), dtype=np.int64),
     )
+    return res
 
 
 @jit(nopython=True)