diff --git modules/node/node.module modules/node/node.module
index 39a1d3b..7535632 100644
--- modules/node/node.module
+++ modules/node/node.module
@@ -938,36 +938,43 @@ function node_save($node) {
   module_invoke_all('node_presave', $node);
   global $user;
 
+  // Determine if we are inserting a new node.
   if (!isset($node->is_new)) {
     $node->is_new = empty($node->nid);
   }
 
-  // Apply filters to some default node fields:
-  if ($node->is_new) {
-    // Insert a new node.
-    $node->is_new = TRUE;
-
-    // When inserting a node, $node->log must be set because
-    // {node_revision}.log does not (and cannot) have a default
-    // value. If the user does not have permission to create
-    // revisions, however, the form will not contain an element for
-    // log so $node->log will be unset at this point.
+  if ($node->is_new || !empty($node->revision)) {
+    // When inserting a node revision, $node->log must be set because
+    // {node_revision}.log cannot have a default value because it is a text
+    // column. However, $node->log may not be set at this point, such as if the
+    // user submitting a node form does not have permission to create revisions.
     if (!isset($node->log)) {
       $node->log = '';
     }
   }
-  elseif (!empty($node->revision)) {
+  elseif (empty($node->log)) {
+    // When updating, avoid clobbering an existing log entry with an empty one.
+    unset($node->log);
+  }
+
+  // $node->teaser and $node->body are also text columns and have no default,
+  // but are not allowed to be NULL.
+  // @todo: make these columns nullable since node types are not required to
+  // use them.
+  if (!isset($node->teaser)) {
+    $node->teaser = '';
+  }
+  if (!isset($node->body)) {
+    $node->body = '';
+  }
+
+  // Save the old revision ID for use by node hook implementations.
+  if (!$node->is_new && !empty($node->revision) && $node->vid) {
     $node->old_vid = $node->vid;
     unset($node->vid);
   }
-  else {
-    // When updating a node, avoid clobbering an existing log entry with an empty one.
-    if (empty($node->log)) {
-      unset($node->log);
-    }
-  }
 
-  // Set some required fields:
+  // Set the timestamp fields:
   if (empty($node->created)) {
     $node->created = REQUEST_TIME;
   }
@@ -985,7 +992,7 @@ function node_save($node) {
   $langcode = FIELD_LANGUAGE_NONE;
   $node->title = $title_field[$langcode][0]['value'];
 
-  // Generate the node table query and the node_revisions table query.
+  // Write to the the {node} and {node_revisions} tables.
   if ($node->is_new) {
     drupal_write_record('node', $node);
     _node_save_revision($node, $user->uid);