Dequeísmo is a variation in Spanish grammar

Spanish grammar

Spanish grammar is the grammar of the Spanish language , which is a Romance language that originated in north central Spain and is spoken today throughout Spain, some twenty countries in the Americas, and Equatorial Guinea....

, considered wrong in prescriptive

Linguistic prescription

In linguistics, prescription denotes normative practices on such aspects of language use as spelling, grammar, pronunciation, and syntax. It includes judgments on what usages are socially proper and politically correct...

 works, which consists in using de que instead of just que as the complementizer

Complementizer

In linguistics , a complementizer is a syntactic category roughly equivalent to the term subordinating conjunction in traditional grammar. For example, the word that is generally called a complementizer in English sentences like Mary believes that it is raining...

 introducing a verbal complement clause. For example: Me dijo de que estaba cansado ("He told me that he was tired") is a case of dequeísmo since the usual construct is Me dijo que estaba cansado. Dequeísmo is considered peculiar to less-educated speakers, most probably as an instance of hypercorrection

Hypercorrection

In linguistics or usage, hypercorrection is a non-standard usage that results from the over-application of a perceived rule of grammar or a usage prescription...

.