Unable to get count when variable names has a "-"

One of the queries i'm using has a variable with a "-" and splunk is unable to get me the stats count using the variable. Example : your search | stats count by Order-Type Is there a limitation on the variable names to be used in splunk? Note: I did get the final result by using regex. Example: your search | rex field=_raw "Order-Type\=(?[\"A-Z_ ]+)" | stats count by type