6.     Warrant Liability

There were no warrant liabilities at December 31, 2021.

March 2020 Warrant Amendment

On March 3, 2020, we amended certain outstanding warrants to purchase an aggregate of 385,078 shares of common stock, including the January 2020 Warrants and warrants we issued in connection with a financing in August 2019 (the “August 2019 Warrants”), to modify certain provisions that had required them to be previously classified as liabilities and to enable them to now be classified as equity under the relevant accounting standards. As a result, we reclassified the fair value of the warrants on the date of the amendment from warrant liabilities to additional paid-in capital in the balance sheet and statement of stockholders’ equity and recognized a non-cash loss on changes in the fair value of warrants in the statement of operations and comprehensive loss.

The following table provides a roll forward of the fair value of our warrant liabilities, the fair value of which was determined by Level 3 inputs for the year ended December 31, 2020 (in thousands):

The warrant liability associated with the January 2020 Warrants was classified within Level 3 of the fair value hierarchy. The following table presents the weighted-average key assumptions used to calculate the fair value of the January 2020 Warrants:

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The warrant liability associated with the August 2019 Warrants was classified within Level 3 of the fair value hierarchy. The following table presents the weighted-average key assumptions used to calculate the fair value of the August 2019 Warrants:

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