We establish a strong maximum principle for a nonnegative continuous solution 2117&_mathId=si2.gif&_user=111111111&_pii=S0893965916302117&_rdoc=1&_issn=08939659&md5=a0143cc5bc0cc05936d1b6c3a74f85a8">2117-si2.gif"> of a doubly nonlinear parabolic problem in a space–time cylinder 2117&_mathId=si3.gif&_user=111111111&_pii=S0893965916302117&_rdoc=1&_issn=08939659&md5=f0e0d75510035919c5958d14dca78fa0" title="Click to view the MathML source">Ω×(0,τ) with a domain 2117&_mathId=si4.gif&_user=111111111&_pii=S0893965916302117&_rdoc=1&_issn=08939659&md5=b7a31cd8f34c6c2003cae18af5aa9f8d" title="Click to view the MathML source">Ω⊂RN and a sufficiently short time interval 2117&_mathId=si5.gif&_user=111111111&_pii=S0893965916302117&_rdoc=1&_issn=08939659&md5=00fe588b278a5af5d67a0fc537babd05" title="Click to view the MathML source">(0,τ)⊂(0,T). Our method takes advantage of a nonnegative subsolution derived from an expanding spherical wave.