The present invention provides oligomers that binds RNA that consists of a lower affinity region and a higher affinity region, wherein the monomers in the higher affinity region increases the melting temperature (i.e. affinity) of the oligomer base paired to RNA more than the monomers used in the lower affinity region, wherein said increase in melting temperature is relatively to the alternative use of DNA monomers of the same (base) sequence. The oligomers of the invention are useful for binding to target RNA such as mRNA and non-coding RNA and have the advantage that they will be less prone to off-target binding via the lower affinity region than via the higher affinity region.