diff --git a/.changeset/fix-catalog-strict-mode-write.md b/.changeset/fix-catalog-strict-mode-write.md
new file mode 100644
index 0000000000..4e1e0d434d
--- /dev/null
+++ b/.changeset/fix-catalog-strict-mode-write.md
@@ -0,0 +1,6 @@
+---
+"@pnpm/resolve-dependencies": patch
+"pnpm": patch
+---
+
+Fixed a bug where `catalogMode: strict` would write the literal string `"catalog:"` to `pnpm-workspace.yaml` instead of the resolved version specifier when re-adding an existing catalog dependency [#10176](https://github.com/pnpm/pnpm/issues/10176).
diff --git a/pkg-manager/core/test/catalogs.ts b/pkg-manager/core/test/catalogs.ts
index b234ab97cb..95de2e60f2 100644
--- a/pkg-manager/core/test/catalogs.ts
+++ b/pkg-manager/core/test/catalogs.ts
@@ -1340,6 +1340,65 @@ describe('add', () => {
     })
   })
 
+  // Regression test for https://github.com/pnpm/pnpm/issues/10176
+  // When re-adding a dependency that already exists in the catalog with catalogMode: strict,
+  // the catalog entry should preserve the original version specifier, not become 'catalog:'
+  test('re-adding existing catalog dependency with catalogMode: strict preserves catalog specifier', async () => {
+    const { options, projects, readLockfile } = preparePackagesAndReturnObjects([{
+      name: 'project1',
+      dependencies: {
+        'is-positive': 'catalog:',
+      },
+    }])
+
+    // First, install the existing dependency with the catalog
+    const mutateOpts = {
+      ...options,
+      lockfileOnly: true,
+      catalogs: {
+        default: { 'is-positive': '^1.0.0' },
+      },
+      catalogMode: 'strict' as const,
+    }
+
+    await mutateModules(installProjects(projects), mutateOpts)
+
+    // Verify initial state
+    expect(readLockfile().catalogs?.default?.['is-positive']).toEqual({
+      specifier: '^1.0.0',
+      version: '1.0.0',
+    })
+
+    // Now re-add the same dependency (simulating 'pnpm add is-positive' from a subpackage)
+    const { updatedManifest, updatedCatalogs } = await addDependenciesToPackage(
+      projects['project1' as ProjectId],
+      ['is-positive'],
+      {
+        ...mutateOpts,
+        dir: path.join(options.lockfileDir, 'project1'),
+        allowNew: true,
+      })
+
+    // The manifest should still use catalog:
+    expect(updatedManifest).toEqual({
+      name: 'project1',
+      dependencies: {
+        'is-positive': 'catalog:',
+      },
+    })
+
+    // The catalog should preserve the original specifier, NOT become 'catalog:'
+    // This is the bug fix - previously it would incorrectly write 'catalog:' to the catalog
+    if (updatedCatalogs?.default?.['is-positive']) {
+      expect(updatedCatalogs.default['is-positive']).not.toBe('catalog:')
+      expect(updatedCatalogs.default['is-positive']).toMatch(/^\^?\d/)
+    }
+
+    // The lockfile should have the correct catalog specifier
+    const lockfile = readLockfile()
+    expect(lockfile.catalogs?.default?.['is-positive']?.specifier).not.toBe('catalog:')
+  })
+
   test('adding with catalogMode: prefer will add to or use from catalog', async () => {
     const { options, projects, readLockfile } = preparePackagesAndReturnObjects([{
       name: 'project1',
diff --git a/pkg-manager/resolve-dependencies/src/index.ts b/pkg-manager/resolve-dependencies/src/index.ts
index 93e5f5f44d..ee0343da12 100644
--- a/pkg-manager/resolve-dependencies/src/index.ts
+++ b/pkg-manager/resolve-dependencies/src/index.ts
@@ -289,9 +289,12 @@ export async function resolveDependencies (
       if (!updateSpec) continue
       const dep = resolvedImporter.directDependencies[i]
       if (dep.catalogLookup == null) continue
+      // If normalizedBareSpecifier isn't defined, this catalog entry was resolved from cache.
+      // Avoid updating the updatedCatalogs map since it is likely unchanged.
+      if (dep.normalizedBareSpecifier == null) continue
       updatedCatalogs ??= {}
       updatedCatalogs[dep.catalogLookup.catalogName] ??= {}
-      updatedCatalogs[dep.catalogLookup.catalogName][dep.alias] = dep.normalizedBareSpecifier ?? dep.catalogLookup.userSpecifiedBareSpecifier
+      updatedCatalogs[dep.catalogLookup.catalogName][dep.alias] = dep.normalizedBareSpecifier
     }
   }