diff --git a/source/include/core_mqtt_serializer.h b/source/include/core_mqtt_serializer.h
index da2e7e4ed..f9d4cf920 100644
--- a/source/include/core_mqtt_serializer.h
+++ b/source/include/core_mqtt_serializer.h
@@ -42,18 +42,6 @@
 #endif
 /* *INDENT-ON */
 
-/* MQTT_DO_NOT_USE_CUSTOM_CONFIG allows building the MQTT library
- * without a custom config. If a custom config is provided, the
- * MQTT_DO_NOT_USE_CUSTOM_CONFIG macro should not be defined. */
-#ifndef MQTT_DO_NOT_USE_CUSTOM_CONFIG
-    /* Include custom config file before other headers. */
-    #include "core_mqtt_config.h"
-#endif
-
-/* Include config defaults header to get default values of configs not
- * defined in core_mqtt_config.h file. */
-#include "core_mqtt_config_defaults.h"
-
 #include "transport_interface.h"
 
 /* MQTT packet types. */
diff --git a/test/unit-test/core_mqtt_utest.c b/test/unit-test/core_mqtt_utest.c
index d647fd2d5..3e506f644 100644
--- a/test/unit-test/core_mqtt_utest.c
+++ b/test/unit-test/core_mqtt_utest.c
@@ -38,6 +38,8 @@
 #include "mock_core_mqtt_serializer.h"
 #include "mock_core_mqtt_state.h"
 
+#include "core_mqtt_config_defaults.h"
+
 /* Set network context to double pointer to buffer (uint8_t**). */
 struct NetworkContext
 {