diff --git a/tls-client/mbedtls_entropy_config.h b/tls-client/mbedtls_entropy_config.h
index 84019cc97..b5dc56fb4 100644
--- a/tls-client/mbedtls_entropy_config.h
+++ b/tls-client/mbedtls_entropy_config.h
@@ -33,6 +33,7 @@
  *  Set this value higher to enable handling larger keys, but be aware that this
  *  will increase the stack usage.
  */
+#undef MBEDTLS_MPI_MAX_SIZE
 #define MBEDTLS_MPI_MAX_SIZE        256
 
 #define MBEDTLS_MPI_WINDOW_SIZE     1