diff --git a/_data/eleventyComputed.js b/_data/eleventyComputed.js
new file mode 100644
index 0000000..2b58219
--- /dev/null
+++ b/_data/eleventyComputed.js
@@ -0,0 +1,33 @@
+/**
+ * Computed data resolved during the data cascade (sequential, per-page).
+ *
+ * Eleventy 3.x renders Nunjucks templates in parallel, which causes
+ * `page.url` and `page.fileSlug` to return wrong values when read
+ * via {% set %} in templates. By computing OG-related values here,
+ * they are resolved before parallel rendering begins.
+ *
+ * See: https://github.com/11ty/eleventy/issues/3183
+ */
+
+import { existsSync } from "node:fs";
+import { resolve, dirname } from "node:path";
+import { fileURLToPath } from "node:url";
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+
+export default {
+  ogSlug: (data) => {
+    const url = data.page?.url;
+    if (!url) return "";
+    return url.replace(/\/$/, "").split("/").pop();
+  },
+
+  hasOgImage: (data) => {
+    const url = data.page?.url;
+    if (!url) return false;
+    const slug = url.replace(/\/$/, "").split("/").pop();
+    if (!slug) return false;
+    const ogPath = resolve(__dirname, "..", ".cache", "og", `${slug}.png`);
+    return existsSync(ogPath);
+  },
+};
diff --git a/_includes/layouts/base.njk b/_includes/layouts/base.njk
index e6d009c..a20af0c 100644
--- a/_includes/layouts/base.njk
+++ b/_includes/layouts/base.njk
@@ -23,16 +23,15 @@
   <meta property="og:type" content="{% if page.url == '/' %}website{% else %}article{% endif %}">
   <meta property="og:description" content="{{ ogDesc }}">
   <meta name="description" content="{{ ogDesc }}">
-  {% set ogFileSlug = page.url | ogSlug %}
-  {% set hasGeneratedOg = ogFileSlug | hasOgImage %}
+  {# ogSlug and hasOgImage are pre-computed via eleventyComputed (race-condition safe) #}
   {% if ogPhoto and ogPhoto != "" and (ogPhoto | length) > 10 %}
   <meta property="og:image" content="{% if 'http' in ogPhoto %}{{ ogPhoto }}{% else %}{{ site.url }}{% if ogPhoto[0] != '/' %}/{% endif %}{{ ogPhoto }}{% endif %}">
   {% elif image and image != "" and (image | length) > 10 %}
   <meta property="og:image" content="{% if 'http' in image %}{{ image }}{% else %}{{ site.url }}{% if image[0] != '/' %}/{% endif %}{{ image }}{% endif %}">
   {% elif contentImage and contentImage != "" and (contentImage | length) > 10 %}
   <meta property="og:image" content="{% if 'http' in contentImage %}{{ contentImage }}{% else %}{{ site.url }}{% if contentImage[0] != '/' %}/{% endif %}{{ contentImage }}{% endif %}">
-  {% elif hasGeneratedOg %}
-  <meta property="og:image" content="{{ site.url }}/og/{{ ogFileSlug }}.png">
+  {% elif hasOgImage %}
+  <meta property="og:image" content="{{ site.url }}/og/{{ ogSlug }}.png">
   {% else %}
   <meta property="og:image" content="{{ site.url }}/images/og-default.png">
   {% endif %}
@@ -41,7 +40,7 @@
   <meta property="og:locale" content="{{ site.locale | default('en_US') }}">
 
   {# Twitter Card meta tags #}
-  {% set hasImage = hasGeneratedOg or (ogPhoto and ogPhoto != "" and (ogPhoto | length) > 10) or (image and image != "" and (image | length) > 10) or (contentImage and contentImage != "" and (contentImage | length) > 10) %}
+  {% set hasImage = hasOgImage or (ogPhoto and ogPhoto != "" and (ogPhoto | length) > 10) or (image and image != "" and (image | length) > 10) or (contentImage and contentImage != "" and (contentImage | length) > 10) %}
   <meta name="twitter:card" content="{% if hasImage %}summary_large_image{% else %}summary{% endif %}">
   <meta name="twitter:title" content="{{ ogTitle }}">
   <meta name="twitter:description" content="{{ ogDesc }}">
@@ -51,8 +50,8 @@
   <meta name="twitter:image" content="{% if 'http' in image %}{{ image }}{% else %}{{ site.url }}/{{ image }}{% endif %}">
   {% elif contentImage and contentImage != "" and (contentImage | length) > 10 %}
   <meta name="twitter:image" content="{% if 'http' in contentImage %}{{ contentImage }}{% else %}{{ site.url }}/{{ contentImage }}{% endif %}">
-  {% elif hasGeneratedOg %}
-  <meta name="twitter:image" content="{{ site.url }}/og/{{ ogFileSlug }}.png">
+  {% elif hasOgImage %}
+  <meta name="twitter:image" content="{{ site.url }}/og/{{ ogSlug }}.png">
   {% endif %}
 
   {# Favicon #}