diff --git a/src/tablecloth/api/join_separate.clj b/src/tablecloth/api/join_separate.clj
index 861aae4..eaf3bdb 100644
--- a/src/tablecloth/api/join_separate.clj
+++ b/src/tablecloth/api/join_separate.clj
@@ -148,10 +148,10 @@
   "
   ([ds src-column opts]
    (assert (not (grouped? ds)) "Not supported on grouped datasets")
-   (let [len-arrays (-> ds src-column first count)
+   (let [len-arrays (-> ds (get src-column) first count)
          new-ds
          (->
-          (dtt/concat-buffers (ds src-column))
+          (dtt/concat-buffers (get ds src-column))
           (tens/reshape [(ds/row-count ds) len-arrays])
           (tech.v3.dataset.tensor/tensor->dataset))
 
diff --git a/test/tablecloth/api/join_separate_test.clj b/test/tablecloth/api/join_separate_test.clj
index aa93bf8..8876315 100644
--- a/test/tablecloth/api/join_separate_test.clj
+++ b/test/tablecloth/api/join_separate_test.clj
@@ -10,7 +10,16 @@
                         :y [:a :b]})
           (api/array-column->columns :x)
           (api/rows :as-maps))
-      => [{:y :a 0 1.0 1 2.0 2 3.0} {:y :b 0 4.0 1 5.0 2 6.0}])
+      => [{:y :a 0 1.0 1 2.0 2 3.0} {:y :b 0 4.0 1 5.0 2 6.0}]
+
+      (-> {"a" [[4 4] [3 2] [2 0]]}
+          api/dataset
+          (api/array-column->columns "a" { :prefix "c"})
+          (api/rows :as-maps)
+          
+          )
+      => [{"c-0" 4, "c-1" 4} {"c-0" 3, "c-1" 2} {"c-0" 2, "c-1" 0}]
+      )
 
 (fact "array-column->columns works can prefix columns with key-word"
       (-> (api/dataset {:x [(double-array [1 2 3])