A search for supersymmetry was performed in events with one electron or muon, jets, and missing transverse momentum. The dataset was the first 5.0 fb-1 of sqrt(s) = 7 TeV proton-proton events from the Large Hadron Collider, as measured by the CMS detector in 2011. A data-driven method was used to estimate the background at high values of the transverse mass, where the suppression of the Standard Model backgrounds allows for relatively loose cuts on the jet activity. No excess above the expected background was observed, so a limit was set in the m0-m1/2 plane of the CMSSM at tan β = 10, A0 = 0, and sgn(μ)=+1.