new file mode 100644
--- /dev/null
+++ b/m4/ftruncate.m4
@@ -0,0 +1,27 @@
+#serial 1
+
+# See if we need to emulate a missing ftruncate function using fcntl.
+
+AC_DEFUN(jm_FUNC_FTRUNCATE,
+[
+  AC_CHECK_FUNCS(ftruncate, , [ftruncate_missing=yes])
+
+  if test "$ftruncate_missing" = yes; then
+    AC_CHECK_HEADERS(unistd.h)
+    AC_MSG_CHECKING([fcntl emulation of ftruncate])
+    AC_CACHE_VAL(fu_cv_sys_ftruncate_emulation,
+    [AC_TRY_LINK([
+#include <sys/types.h>
+#include <fcntl.h>], [
+#if !defined(F_CHSIZE) && !defined(F_FREESP)
+  chsize();
+#endif
+  ],
+      fu_cv_sys_ftruncate_emulation=yes,
+      fu_cv_sys_ftruncate_emulation=no)])
+    AC_MSG_RESULT($fu_cv_sys_ftruncate_emulation)
+    if test $fu_cv_sys_ftruncate_emulation = yes; then
+      LIBOBJS="$LIBOBJS ftruncate.$ac_objext"
+    fi
+  fi
+])