Index: Makefile.in
==================================================================
--- Makefile.in
+++ Makefile.in
@@ -30,11 +30,11 @@
 
 # Create a C-source-ified version of the script resources
 # for TclTLS so that we only need a single file to enable
 # this extension
 @srcdir@/tls.tcl.h: @srcdir@/tls.tcl
-	xxd -i < '@srcdir@/tls.tcl' > '@srcdir@/tls.tcl.h.new'
+	@XXD@ -i < '@srcdir@/tls.tcl' > '@srcdir@/tls.tcl.h.new'
 	mv '@srcdir@/tls.tcl.h.new' '@srcdir@/tls.tcl.h'
 
 # Create default DH parameters
 dh_params.h: @srcdir@/gen_dh_params
 	@srcdir@/gen_dh_params @GEN_DH_PARAMS_ARGS@ > dh_params.h.new

Index: configure.in
==================================================================
--- configure.in
+++ configure.in
@@ -67,10 +67,14 @@
 ])
 if test "$tcltls_debug" = 'true'; then
 	AC_DEFINE(TCLEXT_TCLTLS_DEBUG, [1], [Enable debugging build])
 fi
 
+dnl Find "xxd" so we can build the tls.tcl.h file
+AC_CHECK_TOOL([XXD], [xxd], [__xxd__not__found])
+
+dnl Find "pkg-config" since we need to use it
 AC_CHECK_TOOL([PKGCONFIG], [pkg-config], [false])
 
 dnl XXX:TODO: Automatically determine the SSL library to use
 dnl           defaulting to OpenSSL for compatibility reasons
 if test "$tcltls_ssl_lib" = 'auto'; then