  Cosmic-ray (CR) positrons are relatively rare due to its secondary origin and
thus sensitive to exotic contributions. Primordial black holes (PBHs) with
masses above $\sim 5\times10^{14}\,\mathrm{g}$ can be stable sources of CR
positrons due to Hawking radiation. We show that the CR positron flux measured
by AMS-02 can place stringent constraints on the energy fraction of PBHs
relative to that of dark matter $f_{\text{PBH}}$. Making use of the
state-of-the-art models for CR propagation in both the Galaxy and heliosphere,
we obtain conservative upper limit of $f_{\text{PBH}}\lesssim3\times 10^{-4}$
at $M_{\mathrm{PBH}}\simeq2\times 10^{16}$ g, which improves the previous
constraints obtained from the Voyager CR all-electron data by around an order
of magnitude.
