diff --git a/analysator/vlsvfile/vlsvreader.py b/analysator/vlsvfile/vlsvreader.py
index 12a5f414..281d3556 100644
--- a/analysator/vlsvfile/vlsvreader.py
+++ b/analysator/vlsvfile/vlsvreader.py
@@ -3848,8 +3848,10 @@ def read_velocity_cells(self, cellid, pop="proton"):
 
             if datatype == "float" and element_size == 4:
                data_avgs = np.fromfile(fptr, dtype = np.float32, count = vector_size*num_of_blocks) 
-            if datatype == "float" and element_size == 8:
+            elif datatype == "float" and element_size == 8:
                data_avgs = np.fromfile(fptr, dtype = np.float64, count = vector_size*num_of_blocks) 
+            else:
+               raise TypeError("Error! Bad data type in blocks! datatype found was "+datatype)
             data_avgs = data_avgs.reshape(num_of_blocks, vector_size)
          # Read in block coordinates:
          if ("name" in child.attrib) and (child.attrib["name"] == pop) and (child.tag == "BLOCKIDS"):
@@ -4359,4 +4361,4 @@ def cache_optimization_files(self, force=False):
       ''' Create cached optimization files for this reader object (e.g. spatial index)
       
       '''
-      self.__metadata_cache.set_cellid_spatial_index(force)
\ No newline at end of file
+      self.__metadata_cache.set_cellid_spatial_index(force)