diff --git a/core/cython_types.pyx b/core/cython_types.pyx
index a0fe419..a881016 100644
--- a/core/cython_types.pyx
+++ b/core/cython_types.pyx
@@ -41,13 +41,13 @@ class map:
 		Initialize the map.
 		
 		The source is a sequence of (key, value) tuples.
-		
-		TODO fixme bug
-		>>> map(((1, 2, 3, 4), ('a', 'b', 'c', 'd')))
 		'''
 		
 		if source:
-			self.keys, self.vals = zip(*source)
+			if len(source[0]) == len(source[1]):
+				self.keys, self.vals = source
+			else:
+				raise ValueError('over.core.types.map initialized with two sequences of different lengths')
 		else:
 			self.keys = []
 			self.vals = []
diff --git a/core/python_types.py b/core/python_types.py
index 3fdd7ed..2a4cdeb 100644
--- a/core/python_types.py
+++ b/core/python_types.py
@@ -41,15 +41,13 @@ class map:
 		Initialize the map.
 		
 		The source is a sequence of (key, value) tuples.
-		
-		TODO fixme bug
-		>>> map(((1, 2, 3, 4), ('a', 'b', 'c', 'd')))
 		'''
 		
-		#print(repr(source))
-		
 		if source:
-			self.keys, self.vals = zip(*source)
+			if len(source[0]) == len(source[1]):
+				self.keys, self.vals = source
+			else:
+				raise ValueError('over.core.types.map initialized with two sequences of different lengths')
 		else:
 			self.keys = []
 			self.vals = []