diff --git a/tbl_change.php b/tbl_change.php
index 06c0c553e..dc4ac302f 100644
--- a/tbl_change.php
+++ b/tbl_change.php
@@ -573,7 +573,8 @@ foreach ($loop_array AS $vrowcount => $vrow) {
 
             echo '            <input type="hidden" name="fields_null_prev' . $vkey . '[' . urlencode($field) . ']"';
             if ($real_null_value && !$first_timestamp) {
-                echo ' checked="checked"';
+                //echo ' checked="checked"';
+                echo ' value="on"';
             }
             echo ' />' . "\n";
 
diff --git a/tbl_replace.php b/tbl_replace.php
index 44947c14e..cea073715 100644
--- a/tbl_replace.php
+++ b/tbl_replace.php
@@ -168,13 +168,15 @@ foreach ($loop_array AS $primary_key_index => $enc_primary_key) {
             $cur_value = $me_funcs[$encoded_key] . '(' . $val . '), ';
         }
 
+        //  i n s e r t
         if ($is_insert) {
-            // insert, no need to add column
+            // no need to add column into the valuelist
             $valuelist .= $cur_value;
-        } elseif (isset($me_fields_null_prev) && isset($me_fields_null_prev[$encoded_key]) && !isset($me_fields_null[$encoded_key])) {
-            // field had the null checkbox
+
+        //  u p d a t e
+        } elseif (isset($me_fields_null_prev) && isset($me_fields_null_prev[$encoded_key]) && !empty($me_fields_null_prev[$encoded_key]) && !isset($me_fields_null[$encoded_key])) {
+            // field had the null checkbox before the update
             // field no longer has the null checkbox
-            // field does not have the same value
             $valuelist .= PMA_backquote($key) . ' = ' . $cur_value;
         } elseif (empty($me_funcs[$encoded_key])
             && isset($me_fields_prev) && isset($me_fields_prev[$encoded_key])
@@ -182,8 +184,12 @@ foreach ($loop_array AS $primary_key_index => $enc_primary_key) {
             // No change for this column and no MySQL function is used -> next column
             continue;
         } elseif (!empty($val)) {
-            // TODO: avoid setting a field to NULL when it's already NULL
-            $valuelist .= PMA_backquote($key) . ' = ' . $cur_value;
+            // avoid setting a field to NULL when it's already NULL
+            // (field had the null checkbox before the update
+            //  field still has the null checkbox)
+            if (!(isset($me_fields_null_prev) && isset($me_fields_null_prev[$encoded_key]) && !empty($me_fields_null_prev[$encoded_key]) && isset($me_fields_null[$encoded_key]))) {
+                $valuelist .= PMA_backquote($key) . ' = ' . $cur_value;
+            }
         }
     } // end while