diff --git a/third_party/com/github/bazelbuild/bazel/src/main/protobuf/crosstool_config.proto b/third_party/com/github/bazelbuild/bazel/src/main/protobuf/crosstool_config.proto
index 0a16383..8945755 100644
--- a/third_party/com/github/bazelbuild/bazel/src/main/protobuf/crosstool_config.proto
+++ b/third_party/com/github/bazelbuild/bazel/src/main/protobuf/crosstool_config.proto
@@ -532,7 +532,9 @@
   required string major_version = 1;
   required string minor_version = 2;
 
-  // The default cpu to use if none was specified.
+  // Deprecated. Used to be the default CPU if not otherwise specified, but it's
+  // not used for that purpose (or anything else) anymore. Please also don't add
+  // new uses of this field.
   required string default_target_cpu = 3;
   // The default toolchain to use for each given cpu.
   repeated DefaultCpuToolchain default_toolchain = 4;