diff --git a/.changeset/prompt-input-accept-extensions.md b/.changeset/prompt-input-accept-extensions.md
new file mode 100644
index 00000000..76ac5b6b
--- /dev/null
+++ b/.changeset/prompt-input-accept-extensions.md
@@ -0,0 +1,5 @@
+---
+"ai-elements": patch
+---
+
+Match file extension patterns such as `.pdf` in the PromptInput `accept` prop
diff --git a/apps/docs/content/components/(chatbot)/prompt-input.mdx b/apps/docs/content/components/(chatbot)/prompt-input.mdx
index ad2c9f5b..c8487f80 100644
--- a/apps/docs/content/components/(chatbot)/prompt-input.mdx
+++ b/apps/docs/content/components/(chatbot)/prompt-input.mdx
@@ -283,7 +283,7 @@ Buttons can display tooltips with optional keyboard shortcut hints. Hover over t
     },
     accept: {
       description:
-        'File types to accept (e.g., "image/*"). Leave undefined for any.',
+        'File types to accept, as MIME types or extensions (e.g., "image/*" or ".pdf"). Leave undefined for any.',
       type: "string",
     },
     multiple: {
diff --git a/packages/elements/__tests__/prompt-input.test.tsx b/packages/elements/__tests__/prompt-input.test.tsx
index d961a3ba..6af997a4 100644
--- a/packages/elements/__tests__/prompt-input.test.tsx
+++ b/packages/elements/__tests__/prompt-input.test.tsx
@@ -1685,6 +1685,73 @@ describe("file validation", () => {
     });
   });
 
+  it("matches file extension patterns against the file name", async () => {
+    setupPromptInputTests();
+    const onSubmit = vi.fn();
+    const onError = vi.fn();
+    const user = userEvent.setup();
+
+    // Browsers often report an empty or generic type for these files
+    const sheetFile = new File(["sheet"], "report.xlsx", { type: "" });
+    const csvFile = new File(["a,b"], "DATA.CSV", {
+      type: "application/octet-stream",
+    });
+    const textFile = new File(["text"], "notes.txt", { type: "text/plain" });
+
+    const AttachmentConsumer = () => {
+      const attachments = usePromptInputAttachments();
+      return (
+        <>
+          <button
+            data-testid="add-sheet"
+            onClick={() => attachments.add([sheetFile])}
+            type="button"
+          >
+            Add Sheet
+          </button>
+          <button
+            data-testid="add-csv"
+            onClick={() => attachments.add([csvFile])}
+            type="button"
+          >
+            Add CSV
+          </button>
+          <button
+            data-testid="add-text"
+            onClick={() => attachments.add([textFile])}
+            type="button"
+          >
+            Add Text
+          </button>
+          <div data-testid="count">{attachments.files.length}</div>
+        </>
+      );
+    };
+
+    render(
+      <PromptInput accept=".xlsx, .csv" onError={onError} onSubmit={onSubmit}>
+        <PromptInputBody>
+          <AttachmentConsumer />
+          <PromptInputTextarea />
+        </PromptInputBody>
+      </PromptInput>
+    );
+
+    await user.click(screen.getByTestId("add-sheet"));
+    expect(screen.getByTestId("count")).toHaveTextContent("1");
+
+    await user.click(screen.getByTestId("add-csv"));
+    expect(screen.getByTestId("count")).toHaveTextContent("2");
+    expect(onError).not.toHaveBeenCalled();
+
+    await user.click(screen.getByTestId("add-text"));
+    expect(screen.getByTestId("count")).toHaveTextContent("2");
+    expect(onError).toHaveBeenCalledWith({
+      code: "accept",
+      message: expect.any(String),
+    });
+  });
+
   it("handles accept with extra whitespace in patterns", async () => {
     setupPromptInputTests();
     const onSubmit = vi.fn();
diff --git a/packages/elements/src/prompt-input.tsx b/packages/elements/src/prompt-input.tsx
index 412c846d..8bdf9101 100644
--- a/packages/elements/src/prompt-input.tsx
+++ b/packages/elements/src/prompt-input.tsx
@@ -490,7 +490,7 @@ export type PromptInputProps = Omit<
   HTMLAttributes<HTMLFormElement>,
   "onSubmit" | "onError"
 > & {
-  // e.g., "image/*" or leave undefined for any
+  // e.g., "image/*", ".pdf" or leave undefined for any
   accept?: string;
   multiple?: boolean;
   // When true, accepts drops anywhere on document. Default false (opt-in).
@@ -564,6 +564,10 @@ export const PromptInput = ({
         .filter(Boolean);
 
       return patterns.some((pattern) => {
+        if (pattern.startsWith(".")) {
+          // e.g: .xlsx -> matched against the file name, case-insensitive
+          return f.name.toLowerCase().endsWith(pattern.toLowerCase());
+        }
         if (pattern.endsWith("/*")) {
           // e.g: image/* -> image/
           const prefix = pattern.slice(0, -1);