diff --git a/planner/plansdk/plansdk.go b/planner/plansdk/plansdk.go
index b6ad1245724..646792ee7f5 100644
--- a/planner/plansdk/plansdk.go
+++ b/planner/plansdk/plansdk.go
@@ -51,7 +51,7 @@ type Plan struct {
 	// Ex: python main.py
 	StartStage *Stage `json:"start_stage,omitempty"`
 
-	Definitions []string `cue:"[...string]" json:"definitions"`
+	Definitions []string `cue:"[...string]" json:"definitions,omitempty"`
 	// Errors from plan generation. This usually means
 	// the user application may not be buildable.
 	Errors []PlanError `json:"errors,omitempty"`
diff --git a/testdata/zig/zig-hello-world/plan.json b/testdata/zig/zig-hello-world/plan.json
index b4a1c557b41..f7a9cec944a 100644
--- a/testdata/zig/zig-hello-world/plan.json
+++ b/testdata/zig/zig-hello-world/plan.json
@@ -17,6 +17,5 @@
     "input_files": [
       "./zig-out/bin/"
     ]
-  },
-  "definitions": null
+  }
 }