diff --git a/.changeset/blocker-replay-marker-serializable.md b/.changeset/blocker-replay-marker-serializable.md
new file mode 100644
index 000000000..1bf42430b
--- /dev/null
+++ b/.changeset/blocker-replay-marker-serializable.md
@@ -0,0 +1,5 @@
+---
+"@stackflow/plugin-blocker": patch
+---
+
+Use a namespaced string key instead of a `Symbol` for the internal replay marker. A `Symbol`-keyed property leaked into the recorded event log, so a captured `StackSnapshot` containing a blocked-then-proceeded navigation could not be serialized by codecs that reject symbol keys (e.g. `devalue` throws `Cannot stringify POJOs with symbolic keys`). The marker is now a plain, serializable key.
diff --git a/extensions/plugin-blocker/src/blockerPlugin.ts b/extensions/plugin-blocker/src/blockerPlugin.ts
index 61e0041be..4a6a39ef7 100644
--- a/extensions/plugin-blocker/src/blockerPlugin.ts
+++ b/extensions/plugin-blocker/src/blockerPlugin.ts
@@ -57,7 +57,7 @@ function useBlockerStore(): BlockerStore {
 }
 
 function replayAction(
-  replayMarker: symbol,
+  replayMarker: string,
   store: BlockerStore,
   action: NavigationAction,
 ) {
@@ -92,7 +92,7 @@ function replayAction(
 }
 
 function handleBeforeNavigation(
-  replayMarker: symbol,
+  replayMarker: string,
   store: BlockerStore,
   action: NavigationAction,
   preventDefault: () => void,
@@ -164,7 +164,7 @@ function handleBeforeNavigation(
 export function blockerPlugin(options?: {
   onError?: (error: unknown) => void;
 }): StackflowReactPlugin {
-  const replayMarker = Symbol("@@blockerReplay");
+  const replayMarker = "@stackflow/plugin-blocker/replay";
 
   const store: BlockerStore = {
     blockers: new Map(),