Quorum requirements for a referendum to be valid

Constitution of the Republic of Azerbaijan:

Article139. Invalidity of a Referendum and Invalidation of Referendum Returnsby the Central Election Commission 

139.1.A referendum on issues specified in Articles 3.2 and 153 of the Constitutionof the Republic of Azerbaijan shall be considered invalid, ifless than 25% of voters from the integrated voter list participate in thereferendum. 

139.2.The Central Election Commission shall invalidate the returns of a referendumin the following cases: 

139.2.1.if voting results are considered invalid or when they are cancelledin more than two fifths of the referendum precincts, underthe condition that the number of registered voters in theelection precincts exceeds ? of all voters registered in theconstituency;