diff --git a/commpy/channelcoding/convcode.py b/commpy/channelcoding/convcode.py
index d1dcf16..651913f 100644
--- a/commpy/channelcoding/convcode.py
+++ b/commpy/channelcoding/convcode.py
@@ -521,7 +521,8 @@ def conv_encode(message_bits, trellis, termination = 'term', puncture_matrix=Non
 
     outbits = np.zeros(number_outbits, 'int')
     if puncture_matrix is not None:
-        p_outbits = np.zeros(number_outbits, 'int')
+        number_punctured_bits = int(number_outbits * puncture_matrix.sum() / puncture_matrix.size)
+        p_outbits = np.zeros(number_punctured_bits, 'int')
     else:
         p_outbits = np.zeros(int(number_outbits*
             puncture_matrix[0:].sum()/np.size(puncture_matrix, 1)), 'int')