diff --git a/library/pkcs7.c b/library/pkcs7.c
index 5d470dc..39d9f8f 100644
--- a/library/pkcs7.c
+++ b/library/pkcs7.c
@@ -216,12 +216,11 @@
         return MBEDTLS_ERR_PKCS7_FEATURE_UNAVAILABLE;
     }
 
-    *p = start;
-    if ((ret = mbedtls_x509_crt_parse_der(certs, *p, len1)) < 0) {
+    if ((ret = mbedtls_x509_crt_parse_der(certs, start, len1)) < 0) {
         return MBEDTLS_ERR_PKCS7_INVALID_CERT;
     }
 
-    *p = *p + len1;
+    *p = end_cert;
 
     /*
      * Since in this version we strictly support single certificate, and reaching