diff --git a/R/convenience_cosmx.R b/R/convenience_cosmx.R
index daa92b0b3..e33372bab 100644
--- a/R/convenience_cosmx.R
+++ b/R/convenience_cosmx.R
@@ -906,6 +906,8 @@ setMethod("$<-", signature("CosmxReader"), function(x, name, value) {
 
     if (length(gpolys) > 1L) {
         gpolys <- do.call(rbind, args = gpolys)
+    } else {
+        gpolys <- gpolys[[1]] # unlist
     }
     
     return(gpolys)