grunt-ts: Warning: pattern.indexOf is not a function Use --force to continue.

Trying to run the ts command causes error:

Warning: pattern.indexOf is not a function Use --force to continue.

I tried to debug, but could not find the cause.

grunt-cli v0.1.13 grunt v0.4.5 typescript v1.7.3

Tried all grunt-ts versions until 4.2.0 which worked without issues.

Gruntfile.js configuration:

   ts: {
            development: {
                src: ['src/ts/**/*.ts'],
                outDir: 'src/js',
                options: {
                    module: 'amd',
                    target: 'es5',
                    sourceMap: true,
                    declaration: false,
                    noImplicitAny: false,
                    comments: true
                }
            }
    }

Maybe there’s something I’m missing blindly, but could not find it nor all the results Googling the same error just related mostly to grunt “files” needing to be array of objects instead of object.