diff --git a/lib/BasePipelineSolver.ts b/lib/BasePipelineSolver.ts
index 83219bd..408dc6a 100644
--- a/lib/BasePipelineSolver.ts
+++ b/lib/BasePipelineSolver.ts
@@ -225,7 +225,10 @@ export abstract class BasePipelineSolver<TInput> extends BaseSolver {
    * Get the output from a specific pipeline stage
    */
   getStageOutput<T = any>(stageOutput: string): T | undefined {
-    return this.pipelineOutputs[stageOutput]
+    if (!Object.hasOwn(this.pipelineOutputs, stageOutput)) {
+      return undefined
+    }
+    return this.pipelineOutputs[stageOutput] as T
   }
 
   /**
@@ -239,7 +242,7 @@ export abstract class BasePipelineSolver<TInput> extends BaseSolver {
    * Check if a step has completed and produced output
    */
   hasStageOutput(stageName: string): boolean {
-    return stageName in this.pipelineOutputs
+    return Object.hasOwn(this.pipelineOutputs, stageName)
   }
 
   /**
diff --git a/tests/pipeline-output-lookup.test.ts b/tests/pipeline-output-lookup.test.ts
new file mode 100644
index 0000000..1601ff2
--- /dev/null
+++ b/tests/pipeline-output-lookup.test.ts
@@ -0,0 +1,51 @@
+import { expect, test } from "bun:test"
+import { BasePipelineSolver } from "../lib/BasePipelineSolver"
+import { BaseSolver } from "../lib/BaseSolver"
+
+class EmptyPipeline extends BasePipelineSolver<Record<string, never>> {
+  pipelineDef = []
+}
+
+class ZeroOutputSolver extends BaseSolver {
+  override _step() {
+    this.solved = true
+  }
+
+  override getOutput() {
+    return 0
+  }
+}
+
+class ZeroOutputPipeline extends BasePipelineSolver<Record<string, never>> {
+  zeroSolver?: ZeroOutputSolver
+
+  pipelineDef = [
+    {
+      solverName: "zeroSolver",
+      solverClass: ZeroOutputSolver,
+      getConstructorParams: () => [],
+    },
+  ]
+}
+
+for (const name of ["constructor", "toString", "__proto__"]) {
+  test(`no output exists for inherited Object property ${name}`, () => {
+    const pipeline = new EmptyPipeline({})
+    expect(Object.keys(pipeline.getAllOutputs())).toEqual([])
+    expect(pipeline.hasStageOutput(name)).toBe(false)
+    expect(pipeline.getStageOutput(name)).toBeUndefined()
+  })
+}
+
+test("missing ordinary stage names still report no output", () => {
+  const pipeline = new EmptyPipeline({})
+  expect(pipeline.hasStageOutput("zeroSolver")).toBe(false)
+  expect(pipeline.getStageOutput("zeroSolver")).toBeUndefined()
+})
+
+test("zero-valued completed outputs remain valid", () => {
+  const pipeline = new ZeroOutputPipeline({})
+  pipeline.solve()
+  expect(pipeline.hasStageOutput("zeroSolver")).toBe(true)
+  expect(pipeline.getStageOutput<number>("zeroSolver")).toEqual(0)
+})