diff --git a/python/obitools3/obidms/obidmscolumn/capidmscolumn.pxd b/python/obitools3/obidms/obidmscolumn/capidmscolumn.pxd
index e45f94b..5b242f9 100644
--- a/python/obitools3/obidms/obidmscolumn/capidmscolumn.pxd
+++ b/python/obitools3/obidms/obidmscolumn/capidmscolumn.pxd
@@ -26,7 +26,7 @@ cdef extern from "obidmscolumn.h" nogil:
     ctypedef int32_t obiversion_t
 
     OBIDMS_column_p obi_create_column(OBIDMS_p dms, const char* column_name, OBIType_t type, size_t nb_lines, size_t nb_elements_per_line, const char* elements_names)
-    size_t obi_column_get_line_count(OBIDMS_column_p column)
+    size_t obi_column_get_nb_lines_used(OBIDMS_column_p column)
     const char* obi_column_get_elements_names(OBIDMS_column_p column)
     void obi_column_make_unwritable(OBIDMS_column_p column)
     OBIDMS_column_p obi_open_column(OBIDMS_p dms, const char* column_name, obiversion_t version_number)
diff --git a/python/obitools3/obidms/obidmscolumn/capidmscolumn.pyx b/python/obitools3/obidms/obidmscolumn/capidmscolumn.pyx
index d7a2cec..4ca2cbb 100644
--- a/python/obitools3/obidms/obidmscolumn/capidmscolumn.pyx
+++ b/python/obitools3/obidms/obidmscolumn/capidmscolumn.pyx
@@ -43,8 +43,8 @@ cdef class OBIDMS_column:
             multiple_elements = True
         else :
             element_name = elements_names[0]
-        line_count = obi_column_get_line_count(self.pointer)
-        for line_nb in xrange(line_count):
+        lines_used = obi_column_get_nb_lines_used(self.pointer)
+        for line_nb in xrange(lines_used):
             if multiple_elements :
                 line = []
                 for element_name in elements_names :
diff --git a/src/obidmscolumn.c b/src/obidmscolumn.c
index 00f547e..b4e7075 100644
--- a/src/obidmscolumn.c
+++ b/src/obidmscolumn.c
@@ -1089,6 +1089,12 @@ size_t obi_column_get_line_count(OBIDMS_column_p column)
 }
 
 
+size_t obi_column_get_nb_lines_used(OBIDMS_column_p column)
+{
+	return (column->header)->lines_used;
+}
+
+
 OBIType_t obi_column_get_data_type(OBIDMS_column_p column)
 {
 	return (column->header)->data_type;
diff --git a/src/obidmscolumn.h b/src/obidmscolumn.h
index b431e85..cfe77ec 100644
--- a/src/obidmscolumn.h
+++ b/src/obidmscolumn.h
@@ -243,6 +243,19 @@ void obi_column_make_unwritable(OBIDMS_column_p column);
 size_t obi_column_get_line_count(OBIDMS_column_p column);
 
 
+/**
+ * @brief Recovers the number of lines used in an OBIDMS column.
+ *
+ * @param column a pointer on an OBIDMS column
+ *
+ * @return the number of lines used in the column
+ *
+ * @since August 2015
+ * @author Celine Mercier (celine.mercier@metabarcoding.org)
+ */
+size_t obi_column_get_nb_lines_used(OBIDMS_column_p column);
+
+
 /**
  * @brief Recovers the data type of an OBIDMS column.
  *
diff --git a/src/obidmscolumn_bool.c b/src/obidmscolumn_bool.c
index 22d9ed2..9d5d3c6 100644
--- a/src/obidmscolumn_bool.c
+++ b/src/obidmscolumn_bool.c
@@ -30,7 +30,9 @@
 
 int obi_column_set_bool_with_elt_idx(OBIDMS_column_p column, size_t line_nb, size_t element_idx, obibool_t value)
 {
-	// when/where check if can write?
+	// Update lines used
+	if ((line_nb+1) > (column->header)->lines_used)
+		(column->header)->lines_used = line_nb+1;
 	*(((obibool_t*) (column->data)) + (line_nb * ((column->header)->nb_elements_per_line)) + element_idx) = value;
 	return 0;
 }
diff --git a/src/obidmscolumn_char.c b/src/obidmscolumn_char.c
index 01972d1..88b5ba2 100644
--- a/src/obidmscolumn_char.c
+++ b/src/obidmscolumn_char.c
@@ -30,7 +30,9 @@
 
 int obi_column_set_char_with_elt_idx(OBIDMS_column_p column, size_t line_nb, size_t element_idx, obichar_t* value)
 {
-	// when/where check if can write?
+	// Update lines used
+	if ((line_nb+1) > (column->header)->lines_used)
+		(column->header)->lines_used = line_nb+1;
 	*(((obichar_t*) (column->data)) + (line_nb * ((column->header)->nb_elements_per_line)) + element_idx) = value[0];
 	return 0;
 }
diff --git a/src/obidmscolumn_float.c b/src/obidmscolumn_float.c
index 826aba9..60e1788 100644
--- a/src/obidmscolumn_float.c
+++ b/src/obidmscolumn_float.c
@@ -30,7 +30,9 @@
 
 int obi_column_set_float_with_elt_idx(OBIDMS_column_p column, size_t line_nb, size_t element_idx, obifloat_t value)
 {
-	// when/where check if can write?
+	// Update lines used
+	if ((line_nb+1) > (column->header)->lines_used)
+		(column->header)->lines_used = line_nb+1;
 	*(((obifloat_t*) (column->data)) + (line_nb * ((column->header)->nb_elements_per_line)) + element_idx) = value;
 	return 0;
 }
diff --git a/src/obidmscolumn_idx.c b/src/obidmscolumn_idx.c
index f26ce99..e958d34 100644
--- a/src/obidmscolumn_idx.c
+++ b/src/obidmscolumn_idx.c
@@ -30,7 +30,9 @@
 
 int obi_column_set_idx_with_elt_idx(OBIDMS_column_p column, size_t line_nb, size_t element_idx, obiidx_t value)
 {
-	// when/where check if can write?
+	// Update lines used
+	if ((line_nb+1) > (column->header)->lines_used)
+		(column->header)->lines_used = line_nb+1;
 	*(((obiidx_t*) (column->data)) + (line_nb * ((column->header)->nb_elements_per_line)) + element_idx) = value;
 	return 0;
 }
diff --git a/src/obidmscolumn_int.c b/src/obidmscolumn_int.c
index afd4fb5..15476c2 100644
--- a/src/obidmscolumn_int.c
+++ b/src/obidmscolumn_int.c
@@ -30,7 +30,9 @@
 
 int obi_column_set_int_with_elt_idx(OBIDMS_column_p column, size_t line_nb, size_t element_idx, obiint_t value)
 {
-	// when/where check if can write?
+	// Update lines used
+	if ((line_nb+1) > (column->header)->lines_used)
+		(column->header)->lines_used = line_nb+1;
 	*(((obiint_t*) (column->data)) + (line_nb * ((column->header)->nb_elements_per_line)) + element_idx) = value;
 	return 0;
 }