diff --git a/library/x509_crt.c b/library/x509_crt.c
index e7a98dd..8cb78e5 100644
--- a/library/x509_crt.c
+++ b/library/x509_crt.c
@@ -608,6 +608,11 @@
         *p += len;
     }
 
+    if (*p != end) {
+        return MBEDTLS_ERR_X509_INVALID_EXTENSIONS +
+               MBEDTLS_ERR_ASN1_LENGTH_MISMATCH;
+    }
+
     return 0;
 }