diff --git a/synthpop/ipu/ipu.py b/synthpop/ipu/ipu.py
index 9b225fe..15e99d0 100644
--- a/synthpop/ipu/ipu.py
+++ b/synthpop/ipu/ipu.py
@@ -25,7 +25,7 @@ def for_each_col(col):
         nz = col.to_numpy().nonzero()[0]
         return col.iloc[nz], nz
 
-    for (col_idx, (col, nz)) in df.apply(for_each_col, axis=0, raw=True).items():
+    for (col_idx, (col, nz)) in df.apply(for_each_col, axis=0, raw=False).items():
         yield (col_idx, col, nz)