diff --git a/tools/build_protobuf b/tools/build_protobuf
index b216407c6e..fd2eb5b69b 100755
--- a/tools/build_protobuf
+++ b/tools/build_protobuf
@@ -1,11 +1,15 @@
 #!/bin/bash
 set -e
 
+if [ -n "$1" ]; then
+    OUTDIR=`readlink -f "$1"`
+fi
+
 cd "$(dirname "$0")"
 
 # set up paths
 INDEX="__init__.py"
-GENPATH="../trezorlib/messages"
+GENPATH="${OUTDIR:-../trezorlib/messages}"
 PROTO_PATH="../vendor/trezor-common/protob"
 PROTO_FILES="types messages"