include private pk.h internally

Signed-off-by: Ben Taylor <ben.taylor@linaro.org>
diff --git a/tests/suites/test_suite_x509write.function b/tests/suites/test_suite_x509write.function
index 224768a..49ecc54 100644
--- a/tests/suites/test_suite_x509write.function
+++ b/tests/suites/test_suite_x509write.function
@@ -10,6 +10,9 @@
 #include "mbedtls/asn1.h"
 #include "mbedtls/asn1write.h"
 #include "mbedtls/pk.h"
+#if defined(MBEDTLS_PK_HAVE_PRIVATE_HEADER)
+#include <mbedtls/private/pk_private.h>
+#endif /* MBEDTLS_PK_HAVE_PRIVATE_HEADER */
 #include "mbedtls/psa_util.h"
 
 #if defined(MBEDTLS_USE_PSA_CRYPTO) && \