diff --git a/library/psa_crypto_invasive.h b/library/psa_crypto_invasive.h
index 2b4ee1f..be127d9 100644
--- a/library/psa_crypto_invasive.h
+++ b/library/psa_crypto_invasive.h
@@ -38,6 +38,7 @@
 
 #include "mbedtls/entropy.h"
 
+#if !defined(MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG)
 /** \brief Configure entropy sources.
  *
  * This function may only be called before a call to psa_crypto_init(),
@@ -73,5 +74,6 @@
 psa_status_t mbedtls_psa_crypto_configure_entropy_sources(
     void (* entropy_init )( mbedtls_entropy_context *ctx ),
     void (* entropy_free )( mbedtls_entropy_context *ctx ) );
+#endif /* !defined(MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG) */
 
 #endif /* PSA_CRYPTO_INVASIVE_H */