diff --git a/components/HandleSearchInput.tsx b/components/HandleSearchInput.tsx
index d8efa5b9..91f17691 100644
--- a/components/HandleSearchInput.tsx
+++ b/components/HandleSearchInput.tsx
@@ -1,4 +1,6 @@
 "use client";
+import { useRef } from "react";
+import { isValidHandle } from "@atproto/syntax";
 import { Input } from "components/Input";
 import { Combobox, ComboboxResult } from "components/Combobox";
 import {
@@ -39,6 +41,9 @@ export const HandleSearchInput = (props: {
   // handle was entered); cleared on focus via onFocus.
   highlight?: boolean;
   onFocus?: () => void;
+  // Reject typed values that aren't syntactically valid handles with a native
+  // validation bubble instead of submitting them (suggestion picks are trusted).
+  validateHandle?: boolean;
 }) => {
   let {
     handleValue,
@@ -51,10 +56,23 @@ export const HandleSearchInput = (props: {
     setHighlighted,
   } = useActorTypeahead();
 
+  let triggerRef = useRef<HTMLDivElement>(null);
+
   const handleSelect = async (handle?: string) => {
-    const selected = handle ?? handleValue;
+    let selected = handle ?? handleValue;
     if (!selected) return;
     const actor = suggestions.find((s) => s.handle === selected);
+    if (props.validateHandle && !actor) {
+      selected = selected.trim().replace(/^@/, "");
+      if (!isValidHandle(selected)) {
+        let input = triggerRef.current?.querySelector("input");
+        input?.setCustomValidity(
+          "Please enter a full handle, like name.bsky.social",
+        );
+        input?.reportValidity();
+        return;
+      }
+    }
     setHandleValue(selected);
     setDropdownOpen(false);
     setSuggestions([]);
@@ -87,6 +105,7 @@ export const HandleSearchInput = (props: {
       className="w-(--radix-popover-trigger-width)!"
       trigger={
         <div
+          ref={triggerRef}
           className={`handleInput input-with-border relative py-0! flex items-center gap-2 w-full ${props.large && "px-2!"} ${props.highlight ? INPUT_HIGHLIGHT_CLASS : ""} ${props.className}`}
           style={
             props.loading
@@ -112,6 +131,7 @@ export const HandleSearchInput = (props: {
             size={0}
             value={handleValue}
             onChange={(e) => {
+              e.currentTarget.setCustomValidity("");
               setHandleValue(e.target.value);
               props.onChange?.(e.target.value);
             }}
diff --git a/components/LoginButton.tsx b/components/LoginButton.tsx
index 29cb3d61..944e6cb6 100644
--- a/components/LoginButton.tsx
+++ b/components/LoginButton.tsx
@@ -198,6 +198,7 @@ export const LoginContent = (props: {
               autoFocus={props.open !== false}
               action={<GoToArrow className="text-accent-contrast" />}
               loading={loading}
+              validateHandle
               onSubmit={(handle) => {
                 setLoading(true);
                 window.location.href = buildOauthLoginUrl({
@@ -334,6 +335,7 @@ const LinkAtmosphereContent = (props: {
         autoFocus={props.open !== false}
         action={<GoToArrow className="text-accent-contrast" />}
         loading={loading}
+        validateHandle
         onSubmit={(handle) => {
           setLoading(true);
           window.location.href = buildOauthLoginUrl({