Distribution of the normalised differences in right ascension (left) and declination (right) between the Gaia DR1 positions of 2191 ICRF sources and their radio positions. The histograms are cut at ± 8 in the normalised differences, leaving out 28 sources with | X_α | > 8 and 28 sources with | X_δ | > 8. The black curves are the expected centred normal distribution of unit standard deviation.