Good afternoon, here is something that looks like a bug. A document-command with an _unused_ _trailing_ option swallows the space after it: \documentclass[a6paper,12pt]{scrbook} \usepackage{xparse} \NewDocumentCommand{\myCmd}{ m o }{% \IfValueT{#2}{\typeout{+++#2+++}}% #1% } \begin{document}\Huge This is a \myCmd{test} foo. %spacing wrong This is a \myCmd{test}[bla] foo. %spacing ok \end{document} This behaviour is new and probably not intended. Kind regards, Alexander.