Sumif with multi workbooks

[bobq880]

How can I enter a formula using sumif that uses a second workbook? Example:
=SUMIF([workbook2]'Checking transactions2506'!E1:E110,B5,'[workbook2]Checking transactions2506'!C1:C110)
What is the proper syntax for referencing the second open workbook2?

[SuperTech]

Thank you for the post. Currently it is not possible to use a range from external workbook in function but I have forwarded this as an improvement suggestion.