diff --git a/library/pkcs7.c b/library/pkcs7.c
index 4fdbe36..ec5d569 100644
--- a/library/pkcs7.c
+++ b/library/pkcs7.c
@@ -58,6 +58,9 @@
                                | MBEDTLS_ASN1_CONTEXT_SPECIFIC);
     if (ret != 0) {
         ret = MBEDTLS_ERROR_ADD(MBEDTLS_ERR_PKCS7_INVALID_FORMAT, ret);
+    } else if ((size_t) (end - *p) != *len) {
+        ret = MBEDTLS_ERROR_ADD(MBEDTLS_ERR_PKCS7_INVALID_FORMAT,
+                                MBEDTLS_ERR_ASN1_LENGTH_MISMATCH);
     }
 
     return ret;