diff --git a/packages/happy-server-self-host/scripts/postinstall.cjs b/packages/happy-server-self-host/scripts/postinstall.cjs
index da15805194..449b170048 100644
--- a/packages/happy-server-self-host/scripts/postinstall.cjs
+++ b/packages/happy-server-self-host/scripts/postinstall.cjs
@@ -1,12 +1,13 @@
 'use strict';
 
 /**
- * Generates the Prisma client for installed copies of this package.
+ * Post-install steps for installed copies of this package.
  *
- * prisma/ is a build artifact here — it is copied from packages/happy-server by
- * build-runtime.cjs and only exists in the published tarball. In a fresh
- * monorepo checkout it is absent, so skip rather than fail the workspace
- * install.
+ * 1. Patches pglite-prisma-adapter's Bytes handling. The monorepo applies this
+ *    from patches/fix-pglite-prisma-bytes.cjs via the root postinstall, which
+ *    never runs for consumers who install this package from npm — so it has to
+ *    be applied here too, against whichever copy of the adapter npm resolved.
+ * 2. Generates the Prisma client.
  */
 
 const fs = require('node:fs');
@@ -14,6 +15,57 @@ const path = require('node:path');
 const { spawnSync } = require('node:child_process');
 
 const root = path.resolve(__dirname, '..');
+
+/**
+ * The adapter's parsePgBytes/normalizeByteaArray return Uint8Array, which
+ * serializes as a JSON object {"0":104,"1":101,...} across the JS-WASM boundary
+ * to the Prisma query engine. The engine expects a plain number[] or a base64
+ * string, and rejects the object with P2023 "Inconsistent column data".
+ *
+ * Every Bytes column breaks, which in practice means every dataEncryptionKey:
+ * GET /v1/sessions and GET /v1/machines return 500 as soon as one encrypted
+ * session exists, and no session is ever listed in the app.
+ *
+ * Upstream fix: https://github.com/lucasthevenet/pglite-utils/pull/50
+ */
+function patchPgliteAdapterBytes() {
+  // The adapter exports no './package.json', so resolve its entry point (main,
+  // ./dist/index.cjs) and patch both bundles next to it.
+  let distDir;
+  try {
+    distDir = path.dirname(require.resolve('pglite-prisma-adapter', { paths: [root] }));
+  } catch {
+    return; // not installed yet (e.g. a fresh monorepo checkout)
+  }
+
+  let patched = 0;
+  for (const file of ['index.mjs', 'index.cjs']) {
+    const filePath = path.join(distDir, file);
+    if (!fs.existsSync(filePath)) continue;
+
+    const original = fs.readFileSync(filePath, 'utf8');
+    const content = original.replace(
+      /Uint8Array\.from\(\s*\{\s*length:\s*hexString\.length\s*\/\s*2\s*\}/g,
+      'Array.from({ length: hexString.length / 2 }'
+    );
+
+    if (content !== original) {
+      fs.writeFileSync(filePath, content, 'utf8');
+      patched++;
+    }
+  }
+
+  if (patched > 0) {
+    console.log(`happy-server-self-host: patched pglite-prisma-adapter Bytes handling (${patched} file(s))`);
+  }
+}
+
+patchPgliteAdapterBytes();
+
+// prisma/ is a build artifact here — it is copied from packages/happy-server by
+// build-runtime.cjs and only exists in the published tarball. In a fresh
+// monorepo checkout it is absent, so skip rather than fail the workspace
+// install.
 const schema = path.join(root, 'prisma', 'schema.prisma');
 
 if (!fs.existsSync(schema)) {