  Context. Measurements of the occultation of an exoplanet at visible
wavelengths allow us to determine the reflective properties of a planetary
atmosphere. The observed occultation depth can be translated into a geometric
albedo. This in turn aids in characterising the structure and composition of an
atmosphere by providing additional information on the wavelength-dependent
reflective qualities of the aerosols in the atmosphere.
  Aims. Our aim is to provide a precise measurement of the geometric albedo of
the gas giant HD 189733b by measuring the occultation depth in the broad
optical bandpass of CHEOPS (350 - 1100 nm).
  Methods. We analysed 13 observations of the occultation of HD 189733b
performed by CHEOPS utilising the Python package PyCHEOPS. The resulting
occultation depth is then used to infer the geometric albedo accounting for the
contribution of thermal emission from the planet. We also aid the analysis by
refining the transit parameters combining observations made by the TESS and
CHEOPS space telescopes.
  Results. We report the detection of an $24.7 \pm 4.5$ ppm occultation in the
CHEOPS observations. This occultation depth corresponds to a geometric albedo
of $0.076 \pm 0.016$. Our measurement is consistent with models assuming the
atmosphere of the planet to be cloud-free at the scattering level and
absorption in the CHEOPS band to be dominated by the resonant Na doublet.
Taking into account previous optical-light occultation observations obtained
with the Hubble Space Telescope, both measurements combined are consistent with
a super-stellar Na elemental abundance in the dayside atmosphere of HD 189733b.
We further constrain the planetary Bond albedo to between 0.013 and 0.42 at
3$\sigma$ confidence.
