Clients who invest their retirement accounts in unconventional assets—such as real estate, precious metals, private equity or virtual currency like bitcoin—could be placing their savings at risk, according to a new report.

The report, from the Government Accountability Office, found that retirement accounts allowing such unconventional investments increase the responsibilities of the account owners in ways they may not understand. Those mistakes could trigger additional taxes and tax penalties. On top of that, account custodians can prematurely close an account or let valueless assets and fraud go undetected because they didn’t determine the value of unconventional assets accurately.

In the report, the GAO recommended the IRS improve its guidance for account owners with unconventional retirement assets and clarify how they should annually value these types of assets.

Federal data collection efforts so far have uncovered little information on retirement accounts holding unconventional assets, so the prevalence of such accounts is unknown. In tax year 2015, the IRS started to require custodians or trustees of individual retirement accounts, such as banks, to report selected information on unconventional assets in their clients’ accounts to IRS. Last November, the IRS told the GAO it plans to begin compiling the new IRA asset data in 2017, but it has not specified when the new IRA asset data will be available for analysis.

Seventeen of the 26 custodians identified by the GAO as permitting retirement accounts with unconventional assets, and who participated in the data collection effort, reported having nearly half a million of these accounts in their custody at the end of calendar year 2015. IRAs constituted the vast majority of the accounts and assets reported.

An IRA owner’s decision to invest in unconventional assets can expand their role and responsibilities substantially, the GAO noted. Its review of industry documents found that individuals who wanted to invest in unconventional assets through their IRAs generally agreed to be responsible for overseeing the selection, management and monitoring of account investments and shoulder the consequences of most decisions affecting their accounts. The owners of such accounts thus assume a fiduciary role, which gives them greater responsibility for overseeing the selection, management and monitoring of their account investments, and they shoulder the consequences of most decisions affecting their accounts.

However, the current IRS guidance provides little information to help IRA owners understand their expanded responsibilities and the potential challenges of investing in unconventional assets. Targeted IRS guidance for these IRA owners could help them deal better with the potential compliance challenges associated with certain types of unconventional assets.

The GAO found that some IRA owners can face challenges in monitoring for ongoing federal tax liability. IRA owners are not always aware of the need to monitor the gross income from certain unconventional assets in their accounts for tax liability. For example, IRA owners who invest in active businesses or debt-financed properties need to monitor their accounts for ongoing tax liability that must be paid out of the IRA. Failure to do so can result in underpayment penalties, the GAO noted.

Another problem can arise with obtaining annual fair market valuations for non-publicly traded assets. IRA owners who invest in hard-to-value unconventional assets can face challenges meeting their responsibilities to provide updated fair market value information to their custodian to meet the IRS’s annual reporting requirement. Failure to provide an updated fair market value in a timely manner can lead to a custodian prematurely distributing account assets to the owner at a fair market value that is not current or is potentially incorrect. That could lead to a loss of tax-favored status for their retirement savings.

Federal law places few restrictions on the types of investments allowable in tax-favored retirement accounts, such as IRAs or employer-sponsored 401(k) plans. “Recent federal and state investigations and litigation have raised questions as to whether investing in unconventional assets may jeopardize the accounts’ tax-favored status, placing account owners ’ retirement security at risk,” said the GAO.

The GAO made three recommendations to the IRS, including improving the guidance for account owners with unconventional assets on monitoring for ongoing federal tax liability and to clarify how to determine the fair market value of hard-to-value unconventional assets. The IRS generally agreed with the GAO’s recommendations.

“One of the biggest decisions an IRA owner has to make is how to invest IRA assets,” wrote John M. Dalrymple, deputy commissioner for services and enforcement at the IRS, in response to the report. “IRA owners that invest in unconventional assets could potentially have unforeseen tax liability as well as risk not having sufficient assets to retire.”

Michael Cohn, editor-in-chief of AccountingToday.com, has been covering business and technology for a variety of publications since 1985.