diff --git a/resources/class_cache_handler.php b/resources/class_cache_handler.php
index 3a4bde2..898d9a3 100644
--- a/resources/class_cache_handler.php
+++ b/resources/class_cache_handler.php
@@ -337,7 +337,7 @@ function fid($old_fid)
 			$this->cache_forums();
 		}
 
-		return $this->cache_fids[$old_fid];
+		return isset($this->cache_fids[$old_fid]) ? $this->cache_fids[$old_fid] : 0;
 	}
 
 	/**
@@ -448,7 +448,7 @@ function tid($old_tid)
 			$this->cache_threads();
 		}
 
-		return $this->cache_tids[$old_tid];
+		return isset($this->cache_tids[$old_tid]) ? $this->cache_tids[$old_tid] : 0;
 	}
 
 	/**
diff --git a/resources/functions.php b/resources/functions.php
index bb7cd71..980fff6 100644
--- a/resources/functions.php
+++ b/resources/functions.php
@@ -255,28 +255,11 @@ function delete_import_fields($text=true)
 			$progress += $increment;
 		}
 
-		$columns_to_drop = array();
 		foreach($columns as $column)
 		{
 			if($db->field_exists($column, $table))
 			{
-				$columns_to_drop[] = $column;
-			}
-		}
-		if(!empty($columns_to_drop))
-		{
-			if($db->type == "sqlite")
-			{
-				// Can be achieved in a transaction if we'd finally support it.
-				foreach($columns_to_drop as $column)
-				{
-					$db->write_query("ALTER TABLE ".TABLE_PREFIX.$table." DROP {$column}");
-				}
-			}
-			else
-			{
-				$columns_sql = implode(", DROP ", $columns_to_drop);
-				$db->write_query("ALTER TABLE ".TABLE_PREFIX.$table." DROP {$columns_sql}");
+				$db->drop_column($table, $column);
 			}
 		}
 	}