diff --git a/.changeset/metal-panthers-grow.md b/.changeset/metal-panthers-grow.md
new file mode 100644
index 0000000000..7216d0f0bb
--- /dev/null
+++ b/.changeset/metal-panthers-grow.md
@@ -0,0 +1,5 @@
+---
+"@pnpm/workspace.read-manifest": minor
+---
+
+The type definition for the `packages` field of the `WorkspaceManifest` is now non-null. The `readWorkspaceManifest` function expects this field to be present and throws an error otherwise.
diff --git a/workspace/read-manifest/src/index.ts b/workspace/read-manifest/src/index.ts
index 122ac11e8c..e5511624ca 100644
--- a/workspace/read-manifest/src/index.ts
+++ b/workspace/read-manifest/src/index.ts
@@ -5,7 +5,7 @@ import path from 'node:path'
 import readYamlFile from 'read-yaml-file'
 
 export interface WorkspaceManifest {
-  packages?: string[]
+  packages: string[]
 }
 
 export async function readWorkspaceManifest (dir: string): Promise<WorkspaceManifest | undefined> {