diff --git a/yotta/data/adjust-config.sh b/yotta/data/adjust-config.sh
index 1c10733..9088fd5 100755
--- a/yotta/data/adjust-config.sh
+++ b/yotta/data/adjust-config.sh
@@ -14,9 +14,13 @@
     $SCRIPT -f $FILE $@
 }
 
+# not supported on mbed OS, nor used by mbed Client
 conf unset MBEDTLS_NET_C
 conf unset MBEDTLS_TIMING_C
 
+# not supported on all targets with mbed OS, nor used by mbed Client
+conf unset MBEDTLS_FS_IO
+
 conf unset MBEDTLS_CIPHER_MODE_CFB
 conf unset MBEDTLS_CIPHER_MODE_CTR
 conf unset MBEDTLS_CIPHER_PADDING_ONE_AND_ZEROS