Propriospinal myoclonus is a rare movement disorder characterised by axial flexion or extension myoclonic jerks, produced by activation of spinal segments spreading rostrally or caudally. We present a 54-year-old man with propriospinal myoclonus confirmed on multimodal surface electromyography. Magnetic resonance imaging of his spinal cord was normal. He has a family history of fragile X syndrome and previous screening of his FMR1 gene revealed one allele with 78 CGG triplet repeat expansion, within the premutation range (56–200 repeats). No other cause of his propriospinal myoclonus was found. He responded to 10 mg citalopram. The association with fragile X premutation has only been report in one other patient; treatment with selective serotonin reuptake inhibitors has not been previously reported to our knowledge.