diff --git a/src/registry/report_definition.proto b/src/registry/report_definition.proto
index 43387bc..efcbe92 100644
--- a/src/registry/report_definition.proto
+++ b/src/registry/report_definition.proto
@@ -996,6 +996,9 @@
 // A specification of a field from SystemProfile. These are used in a
 // ReportDefinition to specify which fields should be included in the generated
 // Observations and reports.
+//
+// For a description of the meaning of each field, see the fields in the
+// SystemProfile in: src/pb/common.proto
 enum SystemProfileField {
   OS = 0;
   ARCH = 1;