diff --git a/src/psl.c b/src/psl.c
index 9c3dfc3..899455f 100644
--- a/src/psl.c
+++ b/src/psl.c
@@ -66,6 +66,7 @@
 #include <alloca.h>
 #include <errno.h>
 #include <langinfo.h>
+#include <arpa/inet.h>
 
 #ifdef WITH_LIBICU
 #	include <unicode/uversion.h>
@@ -883,6 +884,15 @@ const char *psl_get_version(void)
 #endif
 }
 
+/* return whether hostname is an IP address or not */
+static int _isip(const char *hostname)
+{
+	struct in_addr addr;
+	struct in6_addr addr6;
+
+	return inet_pton(AF_INET, hostname, &addr) || inet_pton(AF_INET6, hostname, &addr6);
+}
+
 /**
  * psl_is_cookie_domain_acceptable:
  * @psl: PSL context pointer
@@ -920,6 +930,9 @@ int psl_is_cookie_domain_acceptable(const psl_ctx_t *psl, const char *hostname,
 	if (!strcmp(hostname, cookie_domain))
 		return 1; /* an exact match is acceptable (and pretty common) */
 
+	if (_isip(hostname))
+		return 0; /* Hostname is an IP address and these must match fully (RFC 6265, 5.1.3) */
+
 	cookie_domain_length = strlen(cookie_domain);
 	hostname_length = strlen(hostname);
 
diff --git a/tests/test-is-cookie-domain-acceptable.c b/tests/test-is-cookie-domain-acceptable.c
index 79b8f34..dd1f934 100644
--- a/tests/test-is-cookie-domain-acceptable.c
+++ b/tests/test-is-cookie-domain-acceptable.c
@@ -68,6 +68,13 @@ static void test_psl(void)
 		{ "www.example.com", "example.org", 0 },
 		{ "www.sa.gov.au", "sa.gov.au", 0 }, /* not accepted by normalization  (PSL rule '*.ar') */
 		{ "www.educ.ar", "educ.ar", 1 }, /* PSL exception rule '!educ.ar' */
+		/* RFC6265 5.1.3: Having IP addresses, request and domain IP must be identical */
+		{ "192.1.123.2", ".1.123.2", 0 }, /* IPv4 address, partial match */
+		{ "192.1.123.2", "192.1.123.2", 1 }, /* IPv4 address, full match */
+		{ "::1", "::1", 1 }, /* IPv6 address, full match */
+		{ "2a00:1450:4013:c01::8b", ":1450:4013:c01::8b", 0 }, /* IPv6 address, partial match */
+		{ "::ffff:192.1.123.2", "::ffff:192.1.123.2", 1 }, /* IPv6 address dotted-quad, full match */
+		{ "::ffff:192.1.123.2", ".1.123.2", 0 }, /* IPv6 address dotted-quad, partial match */
 	};
 	unsigned it;
 	psl_ctx_t *psl;