The Moscow City Court has ruled that the arrest of Sveltana Davydova, a woman from Vyazma who is accused of treason, was unlawful.
The court on February 16 ruled that Davydova's initial detention in custody from January 22 until February 3 was illegal.
After a public outcry, the mother of seven was freed with travel restrictions on February 3 pending her trial.
The court, however, did not drop the charges against Davydova.
Defense lawyers said they will seek financial compensation from the government for the time of Davydova's illegal detention.
Davydova reportedly telephoned the Ukrainian Embassy in April and told them that soldiers from a base near Vyazma might be being sent to Ukraine.
Based on reporting by RFE/RL's Russian Service and Interfax