diff --git a/python/obitools3/obidms/_obidmscolumn_seq.pyx b/python/obitools3/obidms/_obidmscolumn_seq.pyx
index 7e96eb8..5697619 100644
--- a/python/obitools3/obidms/_obidmscolumn_seq.pyx
+++ b/python/obitools3/obidms/_obidmscolumn_seq.pyx
@@ -27,16 +27,24 @@ cdef class OBIDMS_column_seq(OBIDMS_column):
         if strcmp(value, OBISeq_NA) == 0 :
             result = None
         else :
-            result = <bytes> value
-            free(value)
+            try:
+                result = <bytes> value
+            finally:
+                free(value)
         return result
 
     cpdef set_line(self, index_t line_nb, object value):
         cdef bytes value_b
+
         if value is None :
             value_b = OBISeq_NA
-        else :
+        elif isinstance(value, bytes) :
+            value_b = value
+        elif isinstance(value, str) :
             value_b = str2bytes(value)
+        else:
+            raise TypeError('Sequence value must be of type Bytes, Str or None')
+
         if obi_column_set_obiseq_with_elt_idx_in_view(self.view.pointer, (self.pointer)[0], line_nb, 0, value_b) < 0:
             raise Exception("Problem setting a value in a column")
     
@@ -64,9 +72,10 @@ cdef class OBIDMS_column_multi_elts_seq(OBIDMS_column_multi_elts):
         if strcmp(value, OBISeq_NA) == 0 :
             result = None
         else :
-            result = <bytes> value
-            # Be careful, we have to be sure that the cast copy the data in the python structure
-            free(value)
+            try:
+                result = <bytes> value
+            finally:
+                free(value)
         return result
 
     
@@ -85,8 +94,10 @@ cdef class OBIDMS_column_multi_elts_seq(OBIDMS_column_multi_elts):
             if strcmp(value, OBISeq_NA) == 0 :
                 value_in_result = None
             else :
-                value_in_result = <bytes> value
-                free(value)    
+                try:
+                    value_in_result = <bytes> value
+                finally:
+                    free(value)    
             result[self.elements_names[i]] = value_in_result
             if all_NA and (value_in_result is not None) :
                 all_NA = False