diff --git a/tests/Makefile b/tests/Makefile
index dee011f..2c47634 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -16,6 +16,7 @@
 	LIBRARY_DIR=../src
 	INCLUDE_DIR=-I../inc
 	CFLAGS += "-DMBEDTLS_CONFIG_FILE=\"mbedtls/test_config.h\""
+	CFLAGS += "-DTEST_ENV_MBED_OS"
 endif
 
 LOCAL_CFLAGS = $(WARNING_CFLAGS) $(INCLUDE_DIR) -D_FILE_OFFSET_BITS=64
diff --git a/tests/suites/test_suite_x509parse.function b/tests/suites/test_suite_x509parse.function
index feb8f79..e88f453 100644
--- a/tests/suites/test_suite_x509parse.function
+++ b/tests/suites/test_suite_x509parse.function
@@ -12,7 +12,11 @@
 /* We need to include x509.c because we are testing x509 internal
  * functions from x509_internal.h which are static. With this include
  * we get the tested functions defined. */
+#if defined(TEST_ENV_MBED_OS)
+#include "../src/x509.c"
+#else
 #include "../library/x509.c"
+#endif
 
 #if MBEDTLS_X509_MAX_INTERMEDIATE_CA > 19
 #error "The value of MBEDTLS_X509_MAX_INTERMEDIATE_C is larger \
diff --git a/tests/suites/test_suite_x509write.function b/tests/suites/test_suite_x509write.function
index b0e0969..bd1ddbf 100644
--- a/tests/suites/test_suite_x509write.function
+++ b/tests/suites/test_suite_x509write.function
@@ -9,7 +9,11 @@
 /* We need to include x509.c because we are testing x509 internal
  * functions from x509_internal.h which are static. With this include
  * we get the tested functions defined. */
+#if defined(TEST_ENV_MBED_OS)
+#include "../src/x509.c"
+#else
 #include "../library/x509.c"
+#endif
 
 #if defined(MBEDTLS_RSA_C)
 int mbedtls_rsa_decrypt_func( void *ctx, int mode, size_t *olen,