diff --git a/bids/tsvParser.js b/bids/tsvParser.js
index e7938c4c..e7bc228b 100644
--- a/bids/tsvParser.js
+++ b/bids/tsvParser.js
@@ -15,7 +15,7 @@ const isContentfulRow = (row) => row && !/^\s*$/.test(row)
  * @param {string} contents The contents of a TSV file.
  * @returns {Map<string, string[]>} The parsed contents of the TSV file.
  */
-function parseTSV(contents) {
+export function parseTSV(contents) {
   const columns = new Map()
   const rows = stripBOM(normalizeEOL(contents))
     .split('\n')
@@ -36,5 +36,27 @@ function parseTSV(contents) {
   }
   return columns
 }
+/**
+ * Convert parsed TSV file data from the old BIDS format to the new BIDS format.
+ *
+ * @param {{headers: string[], rows: string[][]}} oldParsedTsv Parsed TSV data using the old format
+ * @returns {Map<string, string[]>} The parsed contents of the TSV file, using the new format.
+ */
+export function convertParsedTSVData(oldParsedTsv) {
+  const columns = new Map()
+
+  oldParsedTsv.headers.forEach((x) => {
+    columns.set(x, [])
+  })
+  for (let i = 1; i < oldParsedTsv.rows.length; i++) {
+    for (let j = 0; j < oldParsedTsv.headers.length; j++) {
+      columns.get(oldParsedTsv.headers[j])?.push(oldParsedTsv.rows[i][j])
+    }
+  }
+  for (const [key, value] of columns) {
+    columns.set(key, value)
+  }
+  return columns
+}
 
 export default parseTSV
diff --git a/bids/types.js b/bids/types.js
index 3a0edc82..f0cdf965 100644
--- a/bids/types.js
+++ b/bids/types.js
@@ -1,6 +1,6 @@
 import { sidecarValueHasHed } from './utils'
 import { generateIssue, Issue } from '../common/issues/issues'
-import parseTSV from './tsvParser'
+import { parseTSV, convertParsedTSVData } from './tsvParser'
 import { parseHedString } from '../parser/main'
 
 /**
@@ -110,17 +110,22 @@ export class BidsTsvFile extends BidsFile {
    * @todo This interface is provisional and subject to modification in version 4.0.0.
    *
    * @param {string} name The name of the TSV file.
-   * @param {Map<string, string[]>|string} tsvData This file's TSV data.
+   * @param {{headers: string[], rows: string[][]}|Map<string, string[]>|string} tsvData This file's TSV data.
    * @param {object} file The file object representing this file.
    * @param {string[]} potentialSidecars The list of potential JSON sidecars.
    * @param {object} mergedDictionary The merged sidecar data.
    */
   constructor(name, tsvData, file, potentialSidecars = [], mergedDictionary = {}) {
     super(name, file)
+    let parsedTsvData
     if (typeof tsvData === 'string') {
-      tsvData = parseTSV(tsvData)
+      parsedTsvData = parseTSV(tsvData)
+    } else if (tsvData === Object(tsvData)) {
+      parsedTsvData = convertParsedTSVData(tsvData)
+    } else {
+      parsedTsvData = tsvData
     }
-    this.parsedTsv = tsvData
+    this.parsedTsv = parsedTsvData
     this.potentialSidecars = potentialSidecars
 
     this.mergedSidecar = new BidsSidecar(name, mergedDictionary, null)
diff --git a/bids/validate.js b/bids/validate.js
index a34f5db9..427c0970 100644
--- a/bids/validate.js
+++ b/bids/validate.js
@@ -362,7 +362,7 @@ class BidsHedValidator {
    */
   _generateTsvSidecarRows(sidecarHedColumns) {
     const sidecarHedRows = []
-    for (const [header, data] of sidecarHedColumns.parsedTsv.entries()) {
+    for (const [header, data] of sidecarHedColumns.entries()) {
       data.forEach((value, index) => {
         if (sidecarHedRows[index] === undefined) {
           sidecarHedRows[index] = new Map()