diff --git a/third_party/systemlibs/protobuf.bzl b/third_party/systemlibs/protobuf.bzl
index bb807e904a3..367ac286395 100644
--- a/third_party/systemlibs/protobuf.bzl
+++ b/third_party/systemlibs/protobuf.bzl
@@ -93,6 +93,7 @@ def _proto_gen_impl(ctx):
         args += ["--python_out=" + gen_dir]
 
     inputs = srcs + deps
+    tools = [ctx.executable.protoc]
     if ctx.executable.plugin:
         plugin = ctx.executable.plugin
         lang = ctx.attr.plugin_language
@@ -106,7 +107,7 @@ def _proto_gen_impl(ctx):
             outdir = ",".join(ctx.attr.plugin_options) + ":" + outdir
         args += ["--plugin=protoc-gen-%s=%s" % (lang, plugin.path)]
         args += ["--%s_out=%s" % (lang, outdir)]
-        inputs += [plugin]
+        tools.append(plugin)
 
     if args:
         ctx.actions.run(
@@ -115,6 +116,7 @@ def _proto_gen_impl(ctx):
             arguments = args + import_flags + [s.path for s in srcs],
             executable = ctx.executable.protoc,
             mnemonic = "ProtoCompile",
+            tools = tools,
             use_default_shell_env = True,
         )