In this paper, we consider optimization of number of secondary users (M) by maximizing average channel throughput of the cognitive radio (CR) network for a given fusion rule (k-out-of-M) at the fusion center (FC) over erroneous control channel. For a given arbitrary positive integer value n, we obtain the mathematical expressions for optimal M for k = 1 + n and k = M-n rules at FC. Considering energy detector as an example for the analysis, following observations are made: 1) In the interval n [0, ⌈M/2⌉-1], as n increases optimal M increases. If FC uses k = 1 + n or k = M-n fusion rule, average channel throughput improves as n increases. 2) For a given n, average channel throughput obtained using k = M-n fusion rule is better compared to k = 1 + n fusion rule. © 2016 IEEE.