diff --git a/.changeset/petite-poets-kneel.md b/.changeset/petite-poets-kneel.md
new file mode 100644
index 00000000..fc63ea05
--- /dev/null
+++ b/.changeset/petite-poets-kneel.md
@@ -0,0 +1,5 @@
+---
+"@browserbasehq/stagehand": minor
+---
+
+support non-string arguments in observations
diff --git a/evals/evals.config.json b/evals/evals.config.json
index f988a3c6..0470cb8a 100644
--- a/evals/evals.config.json
+++ b/evals/evals.config.json
@@ -325,6 +325,10 @@
       "name": "radio_btn",
       "categories": ["act"]
     },
+    {
+      "name": "upload_file",
+      "categories": ["act"]
+    },
     {
       "name": "checkboxes",
       "categories": ["act"]
diff --git a/evals/tasks/upload_file.ts b/evals/tasks/upload_file.ts
new file mode 100644
index 00000000..b60025fc
--- /dev/null
+++ b/evals/tasks/upload_file.ts
@@ -0,0 +1,82 @@
+import { EvalFunction } from "@/types/evals";
+
+export const upload_file: EvalFunction = async ({
+  logger,
+  debugUrl,
+  sessionUrl,
+  stagehand,
+}) => {
+  try {
+    await stagehand.page.goto(
+      "https://browser-tests-alpha.vercel.app/api/upload-test",
+    );
+
+    const observations = await stagehand.page.observe(
+      "Find the element for uploading files",
+    );
+
+    const uploadObservation = observations[0];
+    uploadObservation.arguments = [
+      {
+        name: "emoji.png",
+        mimeType: "image/png",
+        buffer: Buffer.from(
+          "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",
+          "base64",
+        ),
+      },
+    ];
+    uploadObservation.method = "setInputFiles";
+
+    await stagehand.page.act(uploadObservation);
+
+    const actualValue = await stagehand.page
+      .locator("xpath=/html/body/span[2]")
+      .textContent();
+    const expectedValue = "4123";
+
+    await stagehand.close();
+
+    if (actualValue != expectedValue) {
+      return {
+        _success: false,
+        logs: logger.getLogs(),
+        debugUrl,
+        sessionUrl,
+      };
+    }
+
+    return {
+      _success: true,
+      logs: logger.getLogs(),
+      debugUrl,
+      sessionUrl,
+    };
+  } catch (error) {
+    logger.error({
+      message: `error in upload_file function`,
+      level: 0,
+      auxiliary: {
+        error: {
+          value: error.message,
+          type: "string",
+        },
+        trace: {
+          value: error.stack,
+          type: "string",
+        },
+      },
+    });
+
+    await stagehand.close();
+
+    return {
+      _success: false,
+      logs: logger.getLogs(),
+      debugUrl,
+      sessionUrl,
+    };
+  } finally {
+    await stagehand.close();
+  }
+};
diff --git a/lib/handlers/actHandler.ts b/lib/handlers/actHandler.ts
index ae475d0d..ded26119 100644
--- a/lib/handlers/actHandler.ts
+++ b/lib/handlers/actHandler.ts
@@ -244,7 +244,9 @@ export class StagehandActHandler {
       if (actionOrOptions.variables) {
         Object.keys(actionOrOptions.variables).forEach((key) => {
           element.arguments = element.arguments.map((arg) =>
-            arg.replace(`%${key}%`, actionOrOptions.variables![key]),
+            typeof arg === "string"
+              ? arg.replace(`%${key}%`, actionOrOptions.variables![key])
+              : arg,
           );
         });
       }
diff --git a/lib/handlers/handlerUtils/actHandlerUtils.ts b/lib/handlers/handlerUtils/actHandlerUtils.ts
index 1a343389..7ef373e6 100644
--- a/lib/handlers/handlerUtils/actHandlerUtils.ts
+++ b/lib/handlers/handlerUtils/actHandlerUtils.ts
@@ -383,11 +383,15 @@ export async function fallbackLocatorMethod(ctx: MethodHandlerContext) {
   });
 
   try {
+    const locatorMethod = locator[method as keyof Locator];
+    if (typeof locatorMethod !== "function") {
+      throw new PlaywrightCommandException(
+        `Method ${method} is not supported by locator`,
+      );
+    }
     await (
-      locator[method as keyof Locator] as unknown as (
-        ...a: string[]
-      ) => Promise<void>
-    )(...args.map((arg) => arg?.toString() || ""));
+      locatorMethod as unknown as (...a: unknown[]) => Promise<void>
+    ).apply(locator, args as Parameters<typeof locatorMethod>);
   } catch (e) {
     logger({
       category: "action",
diff --git a/types/stagehand.ts b/types/stagehand.ts
index 9d794a69..eaaf0554 100644
--- a/types/stagehand.ts
+++ b/types/stagehand.ts
@@ -152,7 +152,7 @@ export interface ObserveResult {
   description: string;
   backendNodeId?: number;
   method?: string;
-  arguments?: string[];
+  arguments?: unknown[];
 }
 
 export interface LocalBrowserLaunchOptions {