Protein O-fucosyltransferase that specifically catalyzes O- fucosylation of serine or threonine residues in EMI domains of target proteins, such as MMRN1, MMRN2 and EMID1 (PubMed:39775168). Attaches fucose through an O-glycosidic linkage (PubMed:39775168). O- fucosylation of EMI domain-containing proteins may be required for facilitating protein folding and secretion (PubMed:39775168). Also shows minor alpha-(1,3)-fucosyltransferase activity toward activity toward biantennary N-glycan acceptors (PubMed:19088067). However, this was tested with a library of synthetic substrates and this activity is unsure in vivo (PubMed:19088067). {ECO:0000269|PubMed:19088067, ECO:0000269|PubMed:39775168}. This is the function of Ensembl gene identifier ENSG00000196968 (POFUT4, protein O-fucosyltransferase 4).