Index: gawk-5.2.0/support/pma.c
===================================================================
--- gawk-5.2.0.orig/support/pma.c
+++ gawk-5.2.0/support/pma.c
@@ -346,6 +346,7 @@ static void * addrgap(off_t n) {  // fin
   for (U = 1; ; U *= 2)  // double upper bound until failure
     if (MAP_FAILED == (A = MMAP(U))) break;
     else                   MUNMAP(A, U);
+  if (U == 0) U = -1;
   while (1 + L < U) {  // binary search between bounds
     size_t M = L + (U - L) / 2;  // avoid overflow
     if (MAP_FAILED == (A = MMAP(M))) {      U = M; }