diff --git a/Makefile.am b/Makefile.am
index 0426025..90d3597 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -77,6 +77,7 @@ handwritten_tests = \
 	t/parse_assignments.pl \
 	t/skip.pl \
 	t/ssl-validate.pl \
+	t/variable_defaults.pl \
 	t/write_recap.pl
 generated_tests = \
 	t/version.pl
diff --git a/ddclient.in b/ddclient.in
index 3cd9a0c..a415b2a 100755
--- a/ddclient.in
+++ b/ddclient.in
@@ -556,7 +556,7 @@ sub setv {
         'minimum'  => shift,
     };
 }
-my %variables = (
+our %variables = (
     'global-defaults' => {
         'daemon'              => setv(T_DELAY, 0, 0, $daemon_default,      interval('60s')),
         'foreground'          => setv(T_BOOL,  0, 0, 0,                    undef),
@@ -706,7 +706,7 @@ my %variables = (
         'wildcard'            => setv(T_BOOL,  0, 1, 0,                    undef),
     },
 );
-my %protocols = (
+our %protocols = (
     '1984' => {
         'force_update' => undef,
         'update' => \&nic_1984_update,
diff --git a/t/variable_defaults.pl b/t/variable_defaults.pl
new file mode 100644
index 0000000..09dc92c
--- /dev/null
+++ b/t/variable_defaults.pl
@@ -0,0 +1,32 @@
+use Test::More;
+SKIP: { eval { require Test::Warnings; } or skip($@, 1); }
+eval { require 'ddclient'; } or BAIL_OUT($@);
+
+my %variable_collections = (
+    map({ ($_ => $ddclient::variables{$_}) } grep($_ ne 'merged', keys(%ddclient::variables))),
+    map({ ("protocol=$_" => $ddclient::protocols{$_}{variables}); } keys(%ddclient::protocols)),
+);
+my %seen;
+my @test_cases = (
+    map({
+        my $vcn = $_;
+        my $vc = $variable_collections{$_};
+        map({
+            my $def = $vc->{$_};
+            my $seen = exists($seen{$def});
+            $seen{$def} = undef;
+            ({desc => "$vcn $_", def => $vc->{$_}}) x !$seen;
+        } sort(keys(%$vc)));
+    } sort(keys(%variable_collections))),
+);
+for my $tc (@test_cases) {
+    if ($tc->{def}{required}) {
+        is($tc->{def}{default}, undef, "'$tc->{desc}' (required) has no default");
+    } else {
+        my $norm;
+        my $valid = eval { $norm = ddclient::check_value($tc->{def}{default}, $tc->{def}); 1; };
+        ok($valid, "'$tc->{desc}' (optional) has a valid default");
+        is($norm, $tc->{def}{default}, "'$tc->{desc}' default normalizes to itself") if $valid;
+    }
+}
+done_testing();