diff --git a/.changeset/thin-crabs-smoke.md b/.changeset/thin-crabs-smoke.md
new file mode 100644
index 0000000000..3131ab1064
--- /dev/null
+++ b/.changeset/thin-crabs-smoke.md
@@ -0,0 +1,6 @@
+---
+"@pnpm/resolve-dependencies": patch
+"pnpm": patch
+---
+
+Fixed a bug ([#9759](https://github.com/pnpm/pnpm/issues/9759)) where `pnpm add` would incorrectly modify a catalog entry in `pnpm-workspace.yaml` to its exact version.
diff --git a/pkg-manager/core/test/catalogs.ts b/pkg-manager/core/test/catalogs.ts
index 5296fb4d15..492a3f5089 100644
--- a/pkg-manager/core/test/catalogs.ts
+++ b/pkg-manager/core/test/catalogs.ts
@@ -1193,6 +1193,58 @@ describe('add', () => {
     })
   })
 
+  // Regression test for https://github.com/pnpm/pnpm/issues/9759
+  test('adding new usage of default catalog does not mutate catalog entries', async () => {
+    const { options, projects, readLockfile } = preparePackagesAndReturnObjects([
+      {
+        name: 'project1',
+        dependencies: {
+          '@pnpm.e2e/foo': 'catalog:',
+        },
+      },
+      {
+        name: 'project2',
+      },
+    ])
+
+    const catalogs = {
+      default: { '@pnpm.e2e/foo': '^100.0.0' },
+    }
+
+    await mutateModules(installProjects(projects), {
+      ...options,
+      lockfileOnly: true,
+      catalogs,
+    })
+
+    await addDependenciesToPackage(
+      projects['project2' as ProjectId],
+      ['@pnpm.e2e/foo'],
+      {
+        ...options,
+        dir: path.join(options.lockfileDir, 'project2'),
+        lockfileOnly: true,
+        allowNew: true,
+        catalogs,
+      })
+
+    const lockfile = readLockfile()
+
+    // This is the specific condition we're regression testing for. The
+    // specifier used in the original catalog entry should not be modified.
+    expect(lockfile.catalogs.default['@pnpm.e2e/foo'].specifier).toEqual(catalogs.default['@pnpm.e2e/foo'])
+
+    // Sanity check that the rest of the lockfile has expected contents.
+    expect(readLockfile()).toMatchObject({
+      catalogs: { default: { '@pnpm.e2e/foo': { specifier: '^100.0.0', version: '100.0.0' } } },
+      importers: {
+        project1: { dependencies: { '@pnpm.e2e/foo': { specifier: 'catalog:', version: '100.0.0' } } },
+        project2: { dependencies: { '@pnpm.e2e/foo': { specifier: 'catalog:', version: '100.0.0' } } },
+      },
+      packages: { '@pnpm.e2e/foo@100.0.0': expect.any(Object) },
+    })
+  })
+
   test('adding specific version equal to catalog version will use catalog if present', async () => {
     const { options, projects, readLockfile } = preparePackagesAndReturnObjects([{
       name: 'project1',
diff --git a/pkg-manager/resolve-dependencies/src/getExactSinglePreferredVersions.ts b/pkg-manager/resolve-dependencies/src/getExactSinglePreferredVersions.ts
new file mode 100644
index 0000000000..787cc43675
--- /dev/null
+++ b/pkg-manager/resolve-dependencies/src/getExactSinglePreferredVersions.ts
@@ -0,0 +1,13 @@
+import { type PreferredVersions } from '@pnpm/resolver-base'
+import { type WantedDependency } from './getWantedDependencies.js'
+import { unwrapPackageName } from './unwrapPackageName.js'
+
+/**
+ * Create a PreferredVersions object with a specific exact version.
+ */
+export function getExactSinglePreferredVersions (wantedDependency: WantedDependency, version: string): PreferredVersions {
+  const { pkgName } = unwrapPackageName(wantedDependency.alias, wantedDependency.bareSpecifier)
+  return {
+    [pkgName]: { [version]: 'version' },
+  }
+}
diff --git a/pkg-manager/resolve-dependencies/src/resolveDependencies.ts b/pkg-manager/resolve-dependencies/src/resolveDependencies.ts
index 3fa0f33698..ad6c3ff553 100644
--- a/pkg-manager/resolve-dependencies/src/resolveDependencies.ts
+++ b/pkg-manager/resolve-dependencies/src/resolveDependencies.ts
@@ -53,6 +53,7 @@ import pDefer from 'p-defer'
 import pShare from 'promise-share'
 import { pickBy, omit, zipWith } from 'ramda'
 import semver from 'semver'
+import { getExactSinglePreferredVersions } from './getExactSinglePreferredVersions.js'
 import { getNonDevWantedDependencies, type WantedDependency } from './getNonDevWantedDependencies.js'
 import { safeIntersect } from './mergePeers.js'
 import { type NodeId, nextNodeId } from './nextNodeId.js'
@@ -1306,14 +1307,19 @@ async function resolveDependency (
       optional: true,
     }
   }
+
+  // Normalize the `preferredVersion` (singular) and `preferredVersions`
+  // (plural) options. If the singular option is passed through, it'll be used
+  // instead of the plural option.
+  const preferredVersions = !options.updateRequested && options.preferredVersion != null
+    ? getExactSinglePreferredVersions(wantedDependency, options.preferredVersion)
+    : options.preferredVersions
+
   try {
     const calcSpecifier = options.currentDepth === 0
     if (!options.update && currentPkg.version && currentPkg.pkgId?.endsWith(`@${currentPkg.version}`) && !calcSpecifier) {
       wantedDependency.bareSpecifier = replaceVersionInBareSpecifier(wantedDependency.bareSpecifier, currentPkg.version)
     }
-    if (!options.updateRequested && options.preferredVersion != null) {
-      wantedDependency.bareSpecifier = replaceVersionInBareSpecifier(wantedDependency.bareSpecifier, options.preferredVersion)
-    }
     pkgResponse = await ctx.storeController.requestPackage(wantedDependency, {
       allowBuild: ctx.allowBuild,
       alwaysTryWorkspacePackages: ctx.linkWorkspacePackagesDepth >= options.currentDepth,
@@ -1333,7 +1339,7 @@ async function resolveDependency (
       pickLowestVersion: options.pickLowestVersion,
       downloadPriority: -options.currentDepth,
       lockfileDir: ctx.lockfileDir,
-      preferredVersions: options.preferredVersions,
+      preferredVersions,
       preferWorkspacePackages: ctx.preferWorkspacePackages,
       projectDir: (
         options.currentDepth > 0 &&