diff --git a/runtime/vm/service/service.md b/runtime/vm/service/service.md
index 9d90108..f8d56fe 100644
--- a/runtime/vm/service/service.md
+++ b/runtime/vm/service/service.md
@@ -2393,8 +2393,9 @@
   // scripts.
   string source [optional];
 
-  // A table encoding a mapping from token position to line and column.
-  int[][] tokenPosTable;
+  // A table encoding a mapping from token position to line and column. This
+  // field is null if sources aren't available.
+  int[][] tokenPosTable [optional];
 }
 ```
 
diff --git a/runtime/vm/service/service_dev.md b/runtime/vm/service/service_dev.md
index 5d59f09..945d4f9 100644
--- a/runtime/vm/service/service_dev.md
+++ b/runtime/vm/service/service_dev.md
@@ -2393,8 +2393,9 @@
   // scripts.
   string source [optional];
 
-  // A table encoding a mapping from token position to line and column.
-  int[][] tokenPosTable;
+  // A table encoding a mapping from token position to line and column. This
+  // field is null if sources aren't available.
+  int[][] tokenPosTable [optional];
 }
 ```