diff --git a/packages/api/tsdown.config.mjs b/packages/api/tsdown.config.mjs
index 67a8c12136..3a4202e9ec 100644
--- a/packages/api/tsdown.config.mjs
+++ b/packages/api/tsdown.config.mjs
@@ -1,3 +1,4 @@
+import path from 'node:path';
 import { defineConfig } from 'tsdown';
 
 export default defineConfig({
@@ -15,6 +16,6 @@ export default defineConfig({
   // only first-party code: relative imports and the `~/*` tsconfig alias (-> src).
   // `neverBundle` is the 0.22 replacement for the deprecated `external` option.
   deps: {
-    neverBundle: (id) => !id.startsWith('.') && !id.startsWith('~') && !id.startsWith('/'),
+    neverBundle: (id) => !id.startsWith('.') && !id.startsWith('~') && !path.isAbsolute(id),
   },
 });
diff --git a/packages/client/tsdown.config.mjs b/packages/client/tsdown.config.mjs
index cbb178a929..a027189ce6 100644
--- a/packages/client/tsdown.config.mjs
+++ b/packages/client/tsdown.config.mjs
@@ -1,3 +1,4 @@
+import path from 'node:path';
 import { defineConfig } from 'tsdown';
 
 // Mirror the prior Rollup `@rollup/plugin-replace` substitutions: only these three are
@@ -26,7 +27,7 @@ export default defineConfig({
   // Externalize every third-party import (consumers provide the peers + react/jsx-runtime);
   // bundle only relative, `~`-aliased, and absolute sources.
   deps: {
-    neverBundle: (id) => !id.startsWith('.') && !id.startsWith('~') && !id.startsWith('/'),
+    neverBundle: (id) => !id.startsWith('.') && !id.startsWith('~') && !path.isAbsolute(id),
     onlyBundle: false,
   },
 });
diff --git a/packages/data-provider/tsdown.config.mjs b/packages/data-provider/tsdown.config.mjs
index 91c1497a15..a870e0aa43 100644
--- a/packages/data-provider/tsdown.config.mjs
+++ b/packages/data-provider/tsdown.config.mjs
@@ -1,3 +1,4 @@
+import path from 'node:path';
 import { createRequire } from 'node:module';
 import replace from '@rollup/plugin-replace';
 import { defineConfig } from 'tsdown';
@@ -20,7 +21,7 @@ export default defineConfig({
     // Match the prior Rollup build: bundle nothing third-party. Externalize every
     // bare import (deps, peers, and node built-ins like `crypto`); bundle only the
     // package's own relative/aliased modules.
-    neverBundle: (id) => !id.startsWith('.') && !id.startsWith('/') && !id.startsWith('src/'),
+    neverBundle: (id) => !id.startsWith('.') && !path.isAbsolute(id) && !id.startsWith('src/'),
     onlyBundle: false,
   },
   plugins: [
diff --git a/packages/data-schemas/tsdown.config.mjs b/packages/data-schemas/tsdown.config.mjs
index 0159c4ab94..1b6923ce66 100644
--- a/packages/data-schemas/tsdown.config.mjs
+++ b/packages/data-schemas/tsdown.config.mjs
@@ -1,3 +1,4 @@
+import path from 'node:path';
 import { defineConfig } from 'tsdown';
 
 export default defineConfig({
@@ -16,7 +17,7 @@ export default defineConfig({
       !id.startsWith('dotenv/') &&
       !id.startsWith('.') &&
       !id.startsWith('~') &&
-      !id.startsWith('/'),
+      !path.isAbsolute(id),
     // dotenv is bundled on purpose, so silence the "detected dependencies in bundle" hint.
     onlyBundle: false,
   },