  Blazars are often characterized by a spectral break at soft X-rays, whose
origin is still debated. While most sources show a flattening, some exhibit a
blackbody-like soft excess with temperatures of the order of $\sim$0.1 keV,
similar to low-luminosity, non-jetted Seyferts. Here we present the analysis of
the simultaneous XMM-Newton and NuSTAR observation of the luminous FSRQ
4C+25.05 ($z=2.368$). The observed 0.3-30 keV spectrum is best described by the
sum of a hard X-ray power law ($\Gamma = 1.38_{-0.03}^{+0.05}$) and a soft
component, approximated by a blackbody with $kT_{\rm BB} =
0.66_{-0.04}^{+0.05}$ keV (rest frame). If the spectrum of 4C+25.05 is
interpreted in the context of bulk Comptonization by cold electrons of
broad-line region photons emitted in the direction of the jet, such an unusual
temperature implies a bulk Lorentz factor of the jet of $\Gamma_{\rm bulk}\sim
11.7$. Bulk Comptonization is expected to be ubiquitous on physical grounds,
yet no clear signature of it has been found so far, possibly due to its
transient nature and the lack of high-quality, broad-band X-ray spectra.
