diff --git a/allel/model/dask.py b/allel/model/dask.py
index 50639818..11462005 100644
--- a/allel/model/dask.py
+++ b/allel/model/dask.py
@@ -318,7 +318,8 @@ def __getitem__(self, item):
         return index_genotype_array(self, item, array_cls=type(self),
                                     vector_cls=GenotypeDaskVector)
 
-    def _method(self, method_name, chunks=None, drop_axis=None, dtype=None, **kwargs):
+    def _method(self, method_name, chunks=None, drop_axis=None, new_axis=None, dtype=None,
+                **kwargs):
         if chunks is None:
             # no shape change
             chunks = self.chunks
@@ -330,7 +331,8 @@ def f(block):
                 g = array_cls(block)
                 method = getattr(g, method_name)
                 return method(**kwargs)
-            out = da.map_blocks(f, self.values, drop_axis=drop_axis, dtype=dtype)
+            out = da.map_blocks(f, self.values, chunks=chunks, drop_axis=drop_axis,
+                                new_axis=new_axis, dtype=dtype)
 
         else:
             # map with mask
@@ -340,7 +342,8 @@ def f(block, bmask):
                 method = getattr(g, method_name)
                 return method(**kwargs)
             m = self.mask[:, :, np.newaxis]
-            out = da.map_blocks(f, self.values, m, drop_axis=drop_axis, dtype=dtype)
+            out = da.map_blocks(f, self.values, m, chunks=chunks, drop_axis=drop_axis,
+                                new_axis=new_axis, dtype=dtype)
 
         return out
 
@@ -439,8 +442,10 @@ def to_allele_counts(self, max_allele=None):
         if max_allele is None:
             max_allele = self.max().compute()[()]
 
-        chunks = (self.chunks[0], self.chunks[1], (max_allele + 1,))
-        out = self._method('to_allele_counts', chunks=chunks, max_allele=max_allele)
+        chunks = (self.chunks[0], self.chunks[1], (max_allele + 1, ))
+
+        out = self._method('to_allele_counts', chunks=chunks, max_allele=max_allele,
+                           drop_axis=2, new_axis=2)
         out = GenotypeAlleleCountsDaskArray(out)
         return out
 
diff --git a/docs/release.rst b/docs/release.rst
index d5063d98..27248f6e 100644
--- a/docs/release.rst
+++ b/docs/release.rst
@@ -1,6 +1,16 @@
 Release notes
 =============
 
+.. _release_1.2.1:
+
+v1.2.1
+------
+
+* Fixed a bug in :func:`allel.GenotypeDaskArray.to_allele_counts` 
+  where the shape of the output array was not being determined correctly. 
+  By :user:`Nick Harding <hardingnj>`, :issue:`266`.
+
+
 .. _release_1.2.0:
 
 v1.2.0