diff --git a/src/sbbs3/mailsrvr.c b/src/sbbs3/mailsrvr.c
index 298dd4a933a0657588b06541bfaa4ebe086caafc..d0bd0382a70acab933f671a5beded07cb6b4c9fa 100644
--- a/src/sbbs3/mailsrvr.c
+++ b/src/sbbs3/mailsrvr.c
@@ -570,7 +570,7 @@ static int sockgetrsp_opt(SOCKET socket, CRYPT_SESSION sess, char* rsp, char *op
 		}
 		break;
 	}
-	mopt[3] = ' ';
+	mopt[strlen(rsp)] = ' ';
 	if (strncmp(buf, mopt, moptlen) == 0)
 		ret = 1;
 	free(mopt);