Modified cellulose ethers are obtainable by admixing cellulose ethers having free OH groups with chemical compounds containing at least one aldehyde group and at least one acid group, and then reacting the acid groups and the aldehyde groups with the free OH groups of the cellulose ethers. The cellulose ethers modified in this way are distinguished by an improved lump-free stirrability into water and a salvation delay which can be adjusted in a targeted manner.