diff --git a/Makefile.am b/Makefile.am
index 9503c04..459931e 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -65,6 +65,7 @@ handwritten_tests = \
 	t/builtinfw_query.pl \
 	t/get_ip_from_if.pl \
 	t/geturl_connectivity.pl \
+	t/interval_expired.pl \
 	t/is-and-extract-ipv4.pl \
 	t/is-and-extract-ipv6.pl \
 	t/is-and-extract-ipv6-global.pl \
diff --git a/ddclient.in b/ddclient.in
index f6bf5ae..c0fa54e 100755
--- a/ddclient.in
+++ b/ddclient.in
@@ -104,7 +104,7 @@ my $programd = $0;
 $programd =~ s%^.*/%%;
 my $program = $programd;
 $program =~ s/d$//;
-my $now = time;
+our $now = time;
 my $hostname = hostname();
 
 # subst_var(subst, default) returns subst unless it looks like @foo@ in which case it returns
@@ -140,7 +140,8 @@ $ENV{'PATH'} = (exists($ENV{PATH}) ? "$ENV{PATH}:" : "") . "/sbin:/usr/sbin:/bin
 
 our %globals;
 our %config;
-my ($result, %cache);
+our %cache;
+my $result;
 my $saved_cache;
 my %saved_opt;
 my $daemon;
@@ -2465,6 +2466,8 @@ sub interval {
         $value = $1 * 60*60;
     } elsif ($value =~ /^(\d+)(days|d)/i) {
         $value = $1 * 60*60*24;
+    } elsif ($value =~ qr/^(?:inf(?:init[ye])?|indefinite(?:ly)?|never|forever|always)$/i) {
+        $value = 'inf';
     } elsif ($value !~ /^\d+$/) {
         $value = undef;
     }
@@ -2473,6 +2476,7 @@ sub interval {
 sub interval_expired {
     my ($host, $time, $interval) = @_;
 
+    return 0 if ($config{$host}{$interval} // 0) == 'inf';
     return 1 if !exists $cache{$host};
     return 1 if !exists $cache{$host}{$time}      || !$cache{$host}{$time};
     return 1 if !exists $config{$host}{$interval} || !$config{$host}{$interval};
diff --git a/t/interval_expired.pl b/t/interval_expired.pl
new file mode 100644
index 0000000..1043dea
--- /dev/null
+++ b/t/interval_expired.pl
@@ -0,0 +1,51 @@
+use Test::More;
+SKIP: { eval { require Test::Warnings; } or skip($@, 1); }
+eval { require 'ddclient'; } or BAIL_OUT($@);
+
+my $h = 't/interval_expired.pl';
+
+my $default_now = 1000000000;
+
+my @test_cases = (
+    {
+        interval => 'inf',
+        want => 0,
+    },
+    {
+        now => 'inf',
+        interval => 'inf',
+        want => 0,
+    },
+    {
+        cache => '-inf',
+        interval => 'inf',
+        want => 0,
+    },
+    {
+        cache => undef,  # Falsy cache value.
+        interval => 'inf',
+        want => 0,
+    },
+    {
+        now => 0,
+        cache => 0,  # Different kind of falsy cache value.
+        interval => 'inf',
+        want => 0,
+    },
+);
+
+for my $tc (@test_cases) {
+    $tc->{now} //= $default_now;
+    # For convenience, $tc->{cache} is an offset from $tc->{now}, not an absolute time..
+    my $cachetime = $tc->{now} + $tc->{cache} if defined($tc->{cache});
+    $ddclient::config{$h} = {'interval' => $tc->{interval}};
+    %ddclient::config if 0;  # suppress spurious warning "Name used only once: possible typo"
+    $ddclient::cache{$h} = {'cached-time' => $cachetime} if defined($cachetime);
+    %ddclient::cache if 0;  # suppress spurious warning "Name used only once: possible typo"
+    $ddclient::now = $tc->{now};
+    $ddclient::now if 0; # suppress spurious warning "Name used only once: possible typo"
+    my $desc = "now=$tc->{now}, cache=${\($cachetime // 'undef')}, interval=$tc->{interval}";
+    is(ddclient::interval_expired($h, 'cached-time', 'interval'), $tc->{want}, $desc);
+}
+
+done_testing();