diff --git a/internal/command/format/diff.go b/internal/command/format/diff.go
index 3d08109e54..1c1da14f48 100644
--- a/internal/command/format/diff.go
+++ b/internal/command/format/diff.go
@@ -107,6 +107,11 @@ func ResourceChange(
 		case plans.ResourceInstanceDeleteBecauseNoResourceConfig:
 			buf.WriteString(fmt.Sprintf("\n  # (because %s is not in configuration)", addr.Resource.Resource))
 		case plans.ResourceInstanceDeleteBecauseNoModule:
+			// FIXME: Ideally we'd truncate addr.Module to reflect the earliest
+			// step that doesn't exist, so it's clearer which call this refers
+			// to, but we don't have enough information out here in the UI layer
+			// to decide that; only the "expander" in Terraform Core knows
+			// which module instance keys are actually declared.
 			buf.WriteString(fmt.Sprintf("\n  # (because %s is not in configuration)", addr.Module))
 		case plans.ResourceInstanceDeleteBecauseWrongRepetition:
 			// We have some different variations of this one