diff --git a/library/x509_crt.c b/library/x509_crt.c
index 874d8f6..61929be 100644
--- a/library/x509_crt.c
+++ b/library/x509_crt.c
@@ -2667,7 +2667,6 @@
 
 static int x509_inet_pton_ipv4(const char *src, void *dst)
 {
-    /* note: allows leading 0's, e.g. 000.000.000.000 */
     const unsigned char *p = (const unsigned char *) src;
     uint8_t *res = (uint8_t *) dst;
     uint8_t digit, num_digits = 0;
@@ -2681,6 +2680,13 @@
             if (digit > 9) {
                 break;
             }
+
+            /* Don't allow leading zeroes. These might mean octal format,
+             * which this implementation does not support. */
+            if (octet == 0 && num_digits > 0) {
+                break;
+            }
+
             octet = octet * 10 + digit;
             num_digits++;
             p++;