Two flares with a duration of several hours are reported for the low-mass X
-ray binary 4U 1636-53. The characteristics of these flares (i.e., decay ti
mescales, spectral softening, fluences) are very similar to those of the ve
ry long type I X-ray bursts recently found in several other low-mass X-ray
binaries, suggesting that the flares in 4U 1636-53 are also very long type
I X-ray bursts. This would make this source the fifth to exhibit this pheno
menon and the first one for which multiple bursts have been found. Interest
ingly, all five sources accrete at approximately 10% of the Eddington mass
accretion rate. Although a chance coincidence or a selection effect cannot
be ruled out at present, this correlation is suggestive and might indicate
that such very long type I X-ray bursts can occur only at a narrow range of
mass accretion rates.