Compact dark matter has been efficiently constrained in the M \lesssim 10 M _ { \odot } mass range by null searches for microlensing of stars in nearby galaxies .
Here we propose to probe the mass range M \gtrsim 10 M _ { \odot } by seeking echoes in gamma-ray-burst light curves induced by strong lensing .
We show that strong gravitational lensing of gamma ray bursts ( GRBs ) by massive compact halo objects ( MACHOs ) generates superimposed GRB images with a characteristic time delay of \gtrsim 1 { ms } for M \gtrsim 10 M _ { \odot } .
Using dedicated simulations to capture the relevant phenomenology of the GRB prompt emission , we calculate the signal-to-noise ratio required to detect GRB lensing events as a function of the flux ratio and time delay between the lensed images .
We then analyze existing data from the Fermi/GBM and Swift/BAT instruments to assess their constraining power on the compact dark matter fraction f _ { DM } .
We find that this data is noise limited , and therefore localization-based masking of background photons is a key ingredient .
Future observatories with better sensitivity will be able to probe down to the f _ { DM } \gtrsim 1 \% level across the 10 M _ { \odot } \lesssim M \lesssim 1000 M _ { \odot } mass range .