diff --git a/src/libstrongswan/asn1/asn1.c b/src/libstrongswan/asn1/asn1.c
index 866b3c857..a08ae5aff 100644
--- a/src/libstrongswan/asn1/asn1.c
+++ b/src/libstrongswan/asn1/asn1.c
@@ -203,7 +203,7 @@ char *asn1_oid_to_string(chunk_t oid)
 	size_t len = 64;
 	char buf[len], *pos = buf;
 	int written;
-	u_int val;
+	uint32_t val;
 
 	if (!oid.len)
 	{
@@ -222,7 +222,11 @@ char *asn1_oid_to_string(chunk_t oid)
 
 	while (oid.len)
 	{
-		val = (val << 7) + (u_int)(oid.ptr[0] & 0x7f);
+		if (val > (UINT32_MAX >> 7))
+		{
+			return NULL;
+		}
+		val = (val << 7) + (uint32_t)(oid.ptr[0] & 0x7f);
 
 		if (oid.ptr[0] < 128)
 		{
diff --git a/src/libstrongswan/tests/suites/test_asn1.c b/src/libstrongswan/tests/suites/test_asn1.c
index fc207355d..03a230ae2 100644
--- a/src/libstrongswan/tests/suites/test_asn1.c
+++ b/src/libstrongswan/tests/suites/test_asn1.c
@@ -253,6 +253,7 @@ START_TEST(test_asn1_oid_to_string)
 			chunk_from_chars( 0x0a, 0x64, 0x87, 0x68, 0xce, 0x10, 0x86, 0x8d,
 			0x20, 0xbd, 0x84, 0x40, 0x84, 0xe2, 0xad, 0x00,
 			0xaf, 0xd7, 0xc2, 0x00, 0xff, 0xff, 0xff, 0x7f) },
+		{ NULL, chunk_from_chars( 0x00, 0xff, 0xff, 0xff, 0xff, 0x7f) },
 		{ NULL, chunk_from_chars(
 			0x0a, 0x02, 0x64, 0x87, 0x68, 0xce, 0x10, 0x86, 0x8d, 0x20,
 			0xbd, 0x84, 0x40, 0x84, 0xe2, 0xad, 0x00, 0xaf, 0xd7, 0xc2, 0x00,