diff --git a/tests/suites/test_suite_x509parse.function b/tests/suites/test_suite_x509parse.function
index 8e0312d55..6fa97adf0 100644
--- a/tests/suites/test_suite_x509parse.function
+++ b/tests/suites/test_suite_x509parse.function
@@ -457,7 +457,7 @@ void mbedtls_x509_crt_verify_chain(  char *chain_paths, char *trusted_ca, int fl
     mbedtls_x509_crt_init( &chain );
     mbedtls_x509_crt_init( &trusted );
 
-    while( (act = strsep( &chain_paths, " " )) )
+    while( ( act = strsep( &chain_paths, " " ) ) != NULL )
         TEST_ASSERT( mbedtls_x509_crt_parse_file( &chain, act ) == 0 );
     TEST_ASSERT( mbedtls_x509_crt_parse_file( &trusted, trusted_ca ) == 0 );