diff --git a/tools/build_protobuf b/tools/build_protobuf
index 02c328f33..b216407c6 100755
--- a/tools/build_protobuf
+++ b/tools/build_protobuf
@@ -3,30 +3,46 @@ set -e
 
 cd "$(dirname "$0")"
 
+# set up paths
+INDEX="__init__.py"
 GENPATH="../trezorlib/messages"
-INDEX="$GENPATH/__init__.py"
 PROTO_PATH="../vendor/trezor-common/protob"
 PROTO_FILES="types messages"
-PB2_OUT="pb2"
 
-rm -f "$GENPATH/[A-Z]*.py"
-mkdir -p "$GENPATH"
+# set up temporary directory & cleanup
+TMPDIR=$(mktemp -d)
+function cleanup {
+    rm -r $TMPDIR
+}
+trap cleanup EXIT
 
-cat > "$INDEX" << EOF
+# set up pb2 outdir
+PB2_OUT="$TMPDIR/pb2"
+mkdir -p "$PB2_OUT"
+
+# compile .proto files to python2 modules using google protobuf library
+for file in $PROTO_FILES; do
+    protoc --python_out="$PB2_OUT" -I/usr/include -I"$PROTO_PATH" "$PROTO_PATH/$file.proto"
+done
+
+# create index (__init__.py)
+cat > "$TMPDIR/$INDEX" << EOF
 # Automatically generated by pb2py
 
 EOF
 
-mkdir -p "$PB2_OUT"
-
+# convert google protobuf library to trezor's internal format
 for file in $PROTO_FILES; do
-    # Compile .proto files to python2 modules using google protobuf library
-    protoc --python_out="$PB2_OUT" -I/usr/include -I"$PROTO_PATH" "$PROTO_PATH/$file.proto"
+    ./pb2py -P "trezorlib.protobuf" -p "$PB2_OUT" -l "$TMPDIR/$INDEX" "$file" "$TMPDIR"
 done
 
-for file in $PROTO_FILES; do
-    # Convert google protobuf library to trezor's internal format
-    ./pb2py -P "trezorlib.protobuf" -p "$PB2_OUT" -l "$INDEX" "$file" "$GENPATH"
-done
+# ensure $GENPATH exists and is empty of messages
+mkdir -p "$GENPATH"
+# only remove messages - there could possibly be other files not starting with capital letter
+rm -f "$GENPATH"/[A-Z]*.py
 
-rm -rf "$PB2_OUT"
+# move generated files to the destination
+# (this assumes $INDEX is *.py, otherwise we'd have to add $INDEX separately)
+mv "$TMPDIR"/*.py "$GENPATH"
+
+# the exit trap handles removing the tmp directory