Add config sanity check for !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 6e23379..b793ac0 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -787,7 +787,8 @@
 typedef void mbedtls_ssl_async_cancel_t( mbedtls_ssl_context *ssl );
 #endif /* MBEDTLS_SSL_ASYNC_PRIVATE */
 
-#if defined(MBEDTLS_X509_CRT_PARSE_C)
+#if defined(MBEDTLS_KEY_EXCHANGE__WITH_CERT__ENABLED) &&        \
+    !defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
 #define MBEDTLS_SSL_PEER_CERT_DIGEST_MAX_LEN  48
 #if defined(MBEDTLS_SHA256_C)
 #define MBEDTLS_SSL_PEER_CERT_DIGEST_DFL_TYPE MBEDTLS_MD_SHA256
@@ -799,9 +800,11 @@
 #define MBEDTLS_SSL_PEER_CERT_DIGEST_DFL_TYPE MBEDTLS_MD_SHA1
 #define MBEDTLS_SSL_PEER_CERT_DIGEST_DFL_LEN  20
 #else
+/* This is already checked in check_config.h, but be sure. */
 #error "Bad configuration - need SHA-1, SHA-256 or SHA-512 enabled to compute digest of peer CRT."
 #endif
-#endif /* MBEDTLS_X509_CRT_PARSE_C */
+#endif /* MBEDTLS_KEY_EXCHANGE__WITH_CERT__ENABLED &&
+          !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
 
 /*
  * This structure is used for storing current session data.