diff --git a/devices/statistics_writer/hdf5_writer.py b/devices/statistics_writer/hdf5_writer.py
index 8d89258fe59795fc1f47d11127c93229a7fa1690..5a5eb5ee3fe4d5d05094874d65293ea7fbc68314 100644
--- a/devices/statistics_writer/hdf5_writer.py
+++ b/devices/statistics_writer/hdf5_writer.py
@@ -144,11 +144,11 @@ class hdf5_writer:
 
     def write_sst_matrix(self, current_group):
         # store the SST values
-        current_group.create_dataset(name="sst_values", data=self.current_matrix.parameters["sst_values"])
+        current_group.create_dataset(name="sst_values", data=self.current_matrix.parameters["sst_values"].astype(numpy.float32), compression="gzip")
 
     def write_xst_matrix(self, current_group):
         # requires a function call to transform the xst_blocks in to the right structure
-        current_group.create_dataset(name="xst_values", data=self.current_matrix.xst_values())
+        current_group.create_dataset(name="xst_values", data=self.current_matrix.xst_values().astype(numpy.cfloat), compression="gzip")
 
     def write_bst_matrix(self, current_group):
         raise NotImplementedError("BST values not implemented")