diff --git a/CHANGELOG.md b/CHANGELOG.md
index 81cae77..e94be23 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,13 @@ All notable changes to `@neynar/ui` will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [1.2.2] - 2025-01-20
+
+### Fixed
+- **ResizablePanel**: Fixed "Panel constraints not found" error when using `collapsed` prop on initial render. Now uses proper timing with retry logic to ensure panel is registered before collapse/expand.
+
+---
+
 ## [1.2.1] - 2025-01-20
 
 ### Added
diff --git a/package.json b/package.json
index 27670a2..4d9853f 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@neynar/ui",
-  "version": "1.2.1",
+  "version": "1.2.2",
   "license": "MIT",
   "author": "Neynar Inc.",
   "description": "AI-first React component library for coding agents. LLM-optimized docs, sensible defaults, zero config. Built on shadcn patterns, Base UI, and Tailwind CSS v4.",
diff --git a/src/components/ui/resizable.tsx b/src/components/ui/resizable.tsx
index aed49cc..77117d8 100644
--- a/src/components/ui/resizable.tsx
+++ b/src/components/ui/resizable.tsx
@@ -77,7 +77,7 @@ function ResizablePanel({
   const elementRef = React.useRef<HTMLDivElement>(null);
   const animatedRef = React.useRef(animated);
   const durationRef = React.useRef(duration);
-  const isFirstRender = React.useRef(true);
+  const prevCollapsedRef = React.useRef<boolean | undefined>(undefined);
 
   // Keep the refs in sync with prop changes
   React.useEffect(() => {
@@ -115,27 +115,36 @@ function ResizablePanel({
   React.useEffect(() => {
     if (collapsed === undefined) return;
 
-    // On first render, defer to allow panel registration
-    if (isFirstRender.current) {
-      isFirstRender.current = false;
-      // Use requestAnimationFrame to ensure panel is registered
-      requestAnimationFrame(() => {
+    const isFirstSync = prevCollapsedRef.current === undefined;
+    const hasChanged = collapsed !== prevCollapsedRef.current;
+    prevCollapsedRef.current = collapsed;
+
+    if (!hasChanged && !isFirstSync) return;
+
+    // Helper to safely call collapse/expand with retry logic
+    const syncState = () => {
+      try {
+        const isCurrentlyCollapsed = panelRef.current?.isCollapsed() ?? false;
+        if (collapsed === isCurrentlyCollapsed) return;
+
         if (collapsed) {
-          panelRef.current?.collapse();
+          if (isFirstSync) {
+            // First sync: no animation
+            panelRef.current?.collapse();
+          } else {
+            withTransition(() => panelRef.current?.collapse());
+          }
+        } else {
+          withTransition(() => panelRef.current?.expand());
         }
-      });
-      return;
-    }
-
-    // After first render, check current state before acting
-    const isCurrentlyCollapsed = panelRef.current?.isCollapsed() ?? false;
-    if (collapsed === isCurrentlyCollapsed) return;
-
-    if (collapsed) {
-      withTransition(() => panelRef.current?.collapse());
-    } else {
-      withTransition(() => panelRef.current?.expand());
-    }
+      } catch {
+        // Panel not ready yet, retry after a tick
+        setTimeout(syncState, 0);
+      }
+    };
+
+    // Use setTimeout(0) to ensure we're after the panel group's layout effects
+    setTimeout(syncState, 0);
   }, [collapsed, withTransition]);
 
   return (