Source map errors

[Vidar Tonaas Fauske]

When using the sourcemap option, I get the following error:

START:
14 12 2020 18:24:03.948:INFO [compiler.karma-typescript]: Compiling project using Typescript 3.8.3
14 12 2020 18:24:08.379:INFO [compiler.karma-typescript]: Compiled 6 files in 4403 ms.
Since Acorn 8.0.0, options.ecmaVersion is required.
Defaulting to 2020, but this will stop working in the future.
14 12 2020 18:24:12.843:ERROR [karma-server]: UncaughtException:: property "sourcesContent" already exists on the sourcemap, use set property instead
14 12 2020 18:24:12.847:ERROR [karma-server]: Error: property "sourcesContent" already exists on the sourcemap, use set property instead
    at Converter.addProperty (my_proj\node_modules\convert-source-map\index.js:76:49)
    at SourceMap.loadFileFromComment (my_proj\node_modules\karma-typescript\dist\bundler\source-map.js:84:21)
    at SourceMap.addFile (my_proj\node_modules\karma-typescript\dist\bundler\source-map.js:35:18)
    at my_proj\node_modules\karma-typescript\dist\bundler\bundler.js:180:29
    at Array.forEach (<anonymous>)
    at Bundler.writeMainBundleFile (my_proj\node_modules\karma-typescript\dist\bundler\bundler.js:179:27)
    at my_proj\node_modules\karma-typescript\dist\bundler\bundler.js:123:19
    at wrapper (my_proj\node_modules\karma-typescript\node_modules\async\dist\async.js:268:20)
    at replenish (my_proj\node_modules\karma-typescript\node_modules\async\dist\async.js:435:29)
    at iterateeCallback (my_proj\node_modules\karma-typescript\node_modules\async\dist\async.js:424:21)

The code in question used to work well previously, and everything seems to work as expected when setting sourceMap option to false. I'm also using karma-typescript-es6-transform with this project, and I'm using 5.2.0 of both.