@@ -194,6 +194,18 @@ describe("GeminiHandler", () => {
 			expect(modelInfo.info.tiers).toBeUndefined()
 		})
 
+		it("should not treat Object prototype keys as known models", () => {
+			// `"toString" in geminiModels` is true via the prototype chain, which would
+			// otherwise resolve `info` to a function. An own-property check avoids this.
+			const protoHandler = new GeminiHandler({
+				apiModelId: "toString",
+				geminiApiKey: "test-key",
+			})
+			const modelInfo = protoHandler.getModel()
+			expect(modelInfo.id).toBe(geminiDefaultModelId)
+			expect(modelInfo.info).toBeDefined()
+		})
+
 		it("should exclude apply_diff and include edit in tool preferences", () => {
 			const modelInfo = handler.getModel()
 			expect(modelInfo.info.excludedTools).toContain("apply_diff")
 
@@ -493,7 +493,7 @@ export class GeminiHandler extends BaseProvider implements SingleCompletionHandl
 		let id: string
 		let info: ModelInfo
 
-		if (modelId && modelId in geminiModels) {
+		if (modelId && Object.hasOwn(geminiModels, modelId)) {
 			id = modelId
 			info = geminiModels[modelId as GeminiModelId]
 		} else if (modelId && modelId.toLowerCase().startsWith("gemini-")) {