Prohibiting a constitutional amendment that runs counter to, e.g., its basic principles, basic rights, religion etc.

[e.g. The Constitution of Czech, Article 9] (1) This Constitution may be supplemented or amended only by constitutional acts. (2) Any changes in the essential requirements for a democratic state governed by the rule of law are impermissible. […] [e.g. The Constitution of Romania, Article 152] (1) The provisions of this Constitution with regard to the national, independent, unitary and indivisible character of the Romanian State, the republican form of government, territorial integrity, independence of justice, political pluralism and official language shall not be subject to revision. (2) Likewise, no revision shall be made if it results in the suppression of the citizens' fundamental rights and freedoms, or of the safeguards thereof. […] [e.g. The Constitution of Iran, Article 177] The contents of the Articles of the Constitution related to the Islamic character of the political system; the basis of all the rules and regulations according to Islamic criteria; the religious footing; the objectives of the Islamic Republic of Iran; the democratic character of the government; the wilāyat al-’amr; the Imamate of Ummah; and the administration of the affairs of the country based on national referenda, official religion of Iran [Islam] and the school [Twelver Ja‘fari] are unalterable.