Context. Lightning flashes in Jupiter have been observed by spacecraft orbiting the planet, but so far, they have escaped optical detection from Earth. However, theoretical estimations suggest that these flashes may be detectable by a large telescope if they can be distinguished from the much more intense background of reflected sunlight from the dayside of the planet that is visible from Earth. Aims: Here we attempt such a detection with the 10.4 m Gran Telescopio de Canarias (GTC) telescope. Methods: To increase the signal-to-background ratio of Jovian lightning flashes in the dayside, we used the recently commissioned fast-photometry modes of the GTC together with a tunable narrowband filter centered on the hydrogen Hα line. The observations were then tested to determine whether they contain statistically significant deviations from the expected noise and instrumental artifacts. Results: Our results are consistent with the null hypothesis that lightning flashes were not detected.