Cannot reference column renamed to Week#(2) in Power Query (invalid identifier)

[T1moris]

In Power BI (Power Query), I tried to rename a column and ran into a strange issue.

When I rename the column to Week#(2) , the automatically generated M code is:

Renamed Columns2 =Table.RenameColumns(#"Expanded Maxim",{{"Week#.1", "Week#(#)(2)"}})

Later, when I write a new step and try to reference this column, I always get an “invalid identifier” error, no matter which name I use:

[Week#(2)]

[Week#(#)(2)]

Both give me an error.

Why is Power Query changing the name to Week#(#)(2) internally?

How am I supposed to correctly reference this column in later steps?

Is there something special about the # character or the parentheses in column names in Power Query / M?

Thanks in advance for any explanation or workaround!

[Omid_Motamedise]

Hi @T1moris 

Power Query has two different concepts:

Display name (what you see in the UI) => Week#(2)

M language identifier (what the engine must use internally)

M has strict identifier rules. A column name can be referenced directly only if it: Starts with a letter or underscore and Contains only letters, numbers, and underscores

Your column name: Week#(2) violates three rules: # is special in M ( and ) are not allowed in identifiers

In M: #"Some Text" means “treat this text literally as a name” So when Power Query internally generates: "Week#(#)(2)"

The column name contains literal text Week#(2), and the # itself must be escaped This is not a rename mistake—it’s Power Query protecting itself from syntax errors.

Why do [Week#(2)] and [Week#(#)(2)] both fail?
Because square brackets only work for valid identifiers. This works: [SalesAmount] and This fails: [Week#(2)]

Because Week#(2) is not a valid identifier, even if that looks like the column name.

The CORRECT way to reference this column is: [#"Week#(2)"]

[ronrsnfld]

Because you have "special" characters within your new name, and even nested special characters, you need to escape those characters:

#"Week#(#)(2)"

Example:

[ralf_anton]

Hallo,

wenn Du Sonderzeichen in den Spaltennamen benutzt, müssen diese bei der Auswertung mit #"..." maskiert werden. Beispiel:

#"Umbenannte Spalten" = Table.RenameColumns(Quelle,{{"Woche 2", "Woche #(#)(2)"}}),
wert = #"Umbenannte Spalten"[#"Woche #(#)(2)"]{0}

Im Prinzip analog zur Verwendung bei Abfrageschrittnamen mit Sonder- oder Leerzeichen.

Besser ist es daher, auf Sonder- und Leerzeichen zu verzichten.

[cengizhanarslan]

# and parentheses are the issue, and what you’re seeing is Power Query trying to “escape” characters that have meaning in M.

In M, #(...) is used in special literals (like #date(2025,1,1) or #duration(...)).
So when you put #( inside a column name (Week#(2)), the rename UI tries to escape it and you end up with the weird internal text Week#(#)(2).