diff --git a/acme-tinier.pl b/acme-tinier.pl
index 266e4ac..6ff2a86 100755
--- a/acme-tinier.pl
+++ b/acme-tinier.pl
@@ -34,7 +34,7 @@ my $header = { alg => 'RS256', jwk => { kty => 'RSA',
 	n => b64(pack 'H*', $pub_hex =~ s/\s|://gr)
 }};
 
-my $json = JSON::PP->new->pretty(0);
+my $json = JSON::PP->new->pretty(0)->canonical(1);
 my $thumbprint = b64(sha256($json->encode($header->{jwk})));
 
 # Pipe data through an external program, keeping status in $?