diff --git a/tablib/core.py b/tablib/core.py
index 1214f99..e7b622c 100644
--- a/tablib/core.py
+++ b/tablib/core.py
@@ -22,7 +22,7 @@ class Dataset(object):
 		self.__headers = None
 		
 		# ('title', index) tuples
-		self._seperators = []
+		self._separators = []
 
 		try:
 			self.headers = kwargs['headers']
@@ -36,6 +36,7 @@ class Dataset(object):
 
 		self._register_formats()
 
+		
 	def __len__(self):
 		return self.height
 
@@ -197,24 +198,26 @@ class Dataset(object):
 				self._data = [tuple([row]) for row in col]
 
 
-	def insert_seperator(self, index, text='-'):
-		"""Adds a seperator to Dataset at given index."""
+	def insert_separator(self, index, text='-'):
+		"""Adds a separator to Dataset at given index."""
 
-		if self.height >= index:
-			sep = (index, text)
-			self._seperators.append(sep)
+		sep = (index, text)
+		self._separators.append(sep)
+
+
+	def append_separator(self, text='-'):
+		"""Adds a separator to Dataset."""
+
+		# change offsets if headers are or aren't defined
+		if not self.headers:
+			index = self.height if self.height else 0
 		else:
-			raise InvalidDimensions
+			index = (self.height + 1) if self.height else 1
+
+		self.insert_separator(index, text)
 
 
-	def append_seperator(self, text='-'):
-		"""Adds a seperator to Dataset."""
-		
-		index = self.height if self.headers else (self.height - 1)
-		self.insert_seperator(index, text)
-
-
-	def insert(self, i, row=None, col=None):
+	def insert(self, i, row=None):
 		"""Inserts a row at given position in Dataset"""
 		if row:
 			self._validate(row)