Fixing ISBN Problems in MARC Field 020 Before Koha Import

ISBNs are small pieces of data with a large impact. In Koha, ISBNs can affect searching, duplicate detection, matching rules, vendor record workflows, and patron discovery.

When ISBNs are stored inconsistently in MARC field 020, the catalogue may still import, but search and matching quality can suffer.

This article explains common ISBN problems before Koha import and how MARCReady can help identify and repair them.

Why ISBN quality matters

During migration or batch import, ISBNs often help answer questions such as:

• Does this incoming record already exist?
• Is this record a duplicate?
• Can staff find the title by ISBN?
• Can the OPAC display the ISBN cleanly?
• Can future vendor records match against this title?

If ISBNs are malformed, mixed with qualifiers, or stored in the wrong subfield, Koha may not match or index them as expected.

MARC field 020 in plain language

MARC field 020 stores the International Standard Book Number.

Common subfields include:

A common cleanup task is separating the ISBN itself from notes, qualifiers, prices, or invalid values.

Common ISBN problems

1. Qualifiers mixed into the ISBN

Example problem:

020 ## $a 9780060723804 paperback

Better structure:

020 ## $a 9780060723804 $q paperback

When the qualifier is mixed into $a, matching and validation may fail.

MARCReady automatically separates qualifiers from ISBNs in 020 $a, moving the qualifier text to a $q subfield.

2. ISBN-10 values in 020 $a

Older records often contain ISBN-10 values. MARCReady automatically converts bare ISBN-10 values in 020 $a to ISBN-13 format, and moves the original ISBN-10 to $z as a canceled or invalid identifier.

For example:

Before: 020 ## $a 0060723807
After:  020 ## $a 9780060723807 $z 0060723807

This makes the record consistent with modern ISBN usage while preserving the original value for reference.

3. Invalid ISBN check digits

An ISBN can have the right number of characters but still be invalid because the check digit does not match.

Invalid ISBNs should not be treated the same as valid ISBNs. In MARC21, canceled or invalid ISBNs can be recorded in $z.

MARCReady flags ISBNs that fail check digit validation for librarian review.

4. Multiple ISBNs in one subfield

Example problem:

020 ## $a 9780000000001 9780000000002

Better structure:

020 ## $a 9780000000001
020 ## $a 9780000000002

When multiple ISBNs are combined in one subfield, systems may not be able to treat them as separate identifiers.

5. Punctuation and spacing problems

ISBNs may include hyphens, spaces, or punctuation. Display formatting is different from the stored identifier. For matching and validation, the stored value should be clean and consistent.

6. Invalid ISBNs stored as valid ISBNs

If an ISBN is known to be canceled or invalid, it should not be stored in the same way as a valid ISBN.

How ISBN problems affect Koha

ISBN problems may cause:

• duplicate records during import;
• poor ISBN search results;
• matching rules to fail;
• vendor records not matching existing records;
• confusing OPAC display;
• manual cleanup after migration.

What librarians should still review

Not every ISBN decision is purely technical. Libraries may need to decide:

• whether to keep both ISBN-10 and ISBN-13 forms;
• whether an invalid ISBN should remain in $z;
• whether multiple manifestations should be represented in one record;
• whether two 020 fields both resolving to the same ISBN-13 represent the same or different editions.

MARCReady applies structural repairs and flags issues. Library policy still matters.

Pre-import ISBN checklist

Before importing into Koha:

• Check a sample of 020 fields.
• Look for qualifiers inside $a.
• Check for multiple ISBNs in one subfield.
• Identify invalid ISBNs.
• Confirm whether ISBN-10 and ISBN-13 values are handled consistently.
• Test matching rules on a sample file.
• Review duplicate detection before full import.

Related articles

• Duplicate Records in Koha: Matching Rules, ISBNs, and Control Numbers
• How to Validate MARC Records Before Importing into Koha
• Vendor MARC Records: What to Check Before Importing into Koha
• What MARCReady Can Fix — and What a Librarian Should Still Review