diff --git a/src/file.c b/src/file.c
index 85bf2f8..7533566 100644
--- a/src/file.c
+++ b/src/file.c
@@ -578,28 +578,28 @@ int get_dectris_eiger_pixel_mask(const struct ds_desc_t *desc, int *buffer) {
   int n_filters = H5Pget_nfilters(dcpl);
   H5Z_filter_t    filter_id;
   if (n_filters>0) {
-	unsigned int    flags;
-	size_t          nelmts = 1;
-	unsigned int    values_out[1] = {99};
-	char            filter_name[80];
-	filter_id = H5Pget_filter(dcpl, (unsigned) 0, &flags, &nelmts, values_out, sizeof(filter_name), filter_name, NULL);
-	if (filter_id>=0) {
-	  fprintf(stderr," filter name =\"%s\"\n",filter_name);
-	}
+    unsigned int    flags;
+    size_t          nelmts = 1;
+    unsigned int    values_out[1] = {99};
+    char            filter_name[80];
+    filter_id = H5Pget_filter(dcpl, (unsigned) 0, &flags, &nelmts, values_out, sizeof(filter_name), filter_name, NULL);
+    if (filter_id>=0) {
+      fprintf(stderr," filter name =\"%s\"\n",filter_name);
+    }
   }
 
   err = H5Dread(ds_id, H5T_NATIVE_INT, H5S_ALL, H5S_ALL, H5P_DEFAULT, buffer);
   if (err < 0) {
-	if (n_filters>0) {
-	  ERROR_JUMP(-1, close_dataset, "Error reading detectorSpecific/pixel_mask with filter(s)");
-	}
-	else {
-	  ERROR_JUMP(-1, close_dataset, "Error reading detectorSpecific/pixel_mask");
-	}
+    if (n_filters>0) {
+      ERROR_JUMP(-1, close_dataset, "Error reading detectorSpecific/pixel_mask with filter(s)");
+    }
+    else {
+      ERROR_JUMP(-1, close_dataset, "Error reading detectorSpecific/pixel_mask");
+    }
   }
 
   if (H5Zfilter_avail(BS_H5_FILTER_ID)) {
-	fprintf(stderr," bitshuffle filter is available now since H5Dread (of pixel-mask) triggered loading of the filter.\n");
+    fprintf(stderr," bitshuffle filter is available now since H5Dread (of pixel-mask) triggered loading of the filter.\n");
   }
 
 close_dataset:
@@ -630,9 +630,9 @@ herr_t det_visit_callback(hid_t root_id, const char *name,
 
   /* check for an "NX_class" attribute */
   {
-    int str_size = 0;
-    void *buffer = NULL;
-    hid_t a_id, t_id, mt_id;
+    char* buffer = (char*)malloc(1);
+    buffer[0] = '\0';
+    hid_t a_id, t_id;
     if (H5Aexists(g_id, "NX_class") <= 0) {
       /* not an error - just close group and allow continuation */
       retval = 0;
@@ -652,70 +652,45 @@ herr_t det_visit_callback(hid_t root_id, const char *name,
     if (t_id < 0) {
       ERROR_JUMP(-1, close_attr, "Error getting datatype");
     }
-    if (H5Tis_variable_str(t_id) > 0) {
-      str_size = -1;
-      buffer = malloc(sizeof(char *));
-    } else {
-      str_size = H5Tget_size(t_id);
-      buffer = malloc(str_size + 1);
+
+    H5A_info_t a_info;
+    herr_t err = H5Aget_info(a_id, &a_info);
+    if (err<0) {
+      ERROR_JUMP(-1, close_type,
+                 "Unable to get attribute info for NX_class");
     }
+    else {
+      if (a_info.cset != H5T_CSET_ASCII && a_info.cset != H5T_CSET_UTF8) {
+        fprintf(stderr," %s : NX_class attribute info cset = unknown with size %d\n",name,(int) a_info.data_size);
+      }
+    }
+
+    buffer = (char *)malloc(sizeof(char)*(H5Tget_size(t_id)+1));
     if (!buffer) {
       ERROR_JUMP(-1, close_type, "Error allocating string buffer");
     }
 
-    mt_id = H5Tcopy(H5T_C_S1);
-    if (mt_id < 0) {
-      ERROR_JUMP(-1, free_buffer, "Error creating HDF5 String datatype");
-    }
-    // set the target string type to be one longer than the recorded string
-    // in keeping with the malloc'd buffer - if this is already a null
-    // terminated string then we will just have two nulls, if it is not
-    // then we won't clobber the last char in the buffer with a null in the
-    // H5Aread call
-    if (H5Tset_size(mt_id, str_size == -1 ? H5T_VARIABLE : str_size + 1) < 0) {
-      char message[64];
-      sprintf(message, "Error setting string datatype to size %d", str_size);
-      ERROR_JUMP(-1, close_mtype, message);
-    }
-
-    if (H5Aread(a_id, mt_id, buffer) < 0) {
+    if (H5Aread(a_id, t_id, buffer) < 0) {
       char message[256];
       sprintf(
           message,
           "H5OVisit callback: Error reading NX_class attribute on group %.128s",
           name);
-      ERROR_JUMP(-1, close_mtype, message);
+      ERROR_JUMP(-1, free_buffer, message);
     }
 
-    /* at least one file has been seen where the NX_class attribute was not null
-     * terminated and extraneous bytes where being read by strcmp -  set the end
-     * byte to null
-     */
-
-    if (str_size > 0)
-      ((char *)buffer)[str_size] = '\0';
     /* test for NXdata or NXdetector */
     {
-      char *nxclass = str_size > 0 ? (char *)buffer : *((char **)buffer);
-      if (strcmp("NXdata", nxclass) == 0) {
+      if      (strcmp("NXdata", buffer) == 0) {
         hid_t out_id = H5Gopen(root_id, name, H5P_DEFAULT);
         output_data->nxdata = out_id;
-      } else if (strcmp("NXdetector", nxclass) == 0) {
+      }
+      else if (strcmp("NXdetector", buffer) == 0) {
         hid_t out_id = H5Gopen(root_id, name, H5P_DEFAULT);
         output_data->nxdetector = out_id;
       }
     }
 
-    if (str_size == -1) {
-      hsize_t dims[1] = {1};
-      hid_t s_id = H5Screate_simple(1, dims, NULL);
-      H5Sselect_all(s_id);
-      H5Dvlen_reclaim(mt_id, s_id, H5P_DEFAULT, buffer);
-      H5Sclose(s_id);
-    }
-
-  close_mtype:
-    H5Tclose(mt_id);
   free_buffer:
     free(buffer);
   close_type: