diff --git a/plugin/README.md b/plugin/README.md
index 7375ed0..2c25772 100644
--- a/plugin/README.md
+++ b/plugin/README.md
@@ -126,10 +126,10 @@ svgJar({
   // Default: 'dom'
   target: 'dom' | 'ember' | 'react' | 'preact' | 'vue' | 'solid' | 'web-component',
 
-  // SVGO configuration.
-  // true (default): use baseline config with sensible defaults
+  // SVGO configuration. See "SVGO optimization" below.
+  // true (default): use the baseline config
   // false: disable optimization entirely
-  // object: custom SVGO config, deep-merged with baseline
+  // object: custom SVGO config, used in place of the baseline
   svgo: true,
 
   // Default sprite name for bare SVG imports.
@@ -417,6 +417,21 @@ SVGO runs per-SVG during the `load` phase (not on assembled sprites) to prevent
 
 Runs in both dev and prod so behaviour is consistent.
 
+A custom `svgo` config replaces the baseline config. svg-jar does not merge them. To keep the baseline and add plugins, copy the baseline plugins from `baselineSvgoConfig`:
+
+```ts
+import { baselineSvgoConfig } from '@svg-jar/plugin';
+import svgJar from '@svg-jar/plugin/vite';
+
+svgJar({
+  svgo: {
+    plugins: [...baselineSvgoConfig.plugins, 'removeDimensions'],
+  },
+});
+```
+
+If you write a config without the baseline, keep the `cleanupIds` override from it: `{ name: 'preset-default', params: { overrides: { cleanupIds: { minify: false, remove: false } } } }`. Without it, SVGO shortens IDs in each file to names like `a` and `b`. Icons from different files then use the same IDs in one sprite sheet, and a `url(#a)` reference can point to the gradient or clip path of a different icon.
+
 ### Embedded reference resolution
 
 SVGs containing `<use href="other.svg">` or `<image href="photo.png">` have their references resolved through the bundler's module graph:
diff --git a/plugin/src/core/options.ts b/plugin/src/core/options.ts
index 43336e9..0752275 100644
--- a/plugin/src/core/options.ts
+++ b/plugin/src/core/options.ts
@@ -13,9 +13,10 @@ export interface SvgJarOptions {
 
   /**
    * SVGO configuration.
-   * - `true` (default): use baseline config with sensible defaults
+   * - `true` (default): use `baselineSvgoConfig`
    * - `false`: disable optimization entirely
-   * - object: custom SVGO config, deep-merged with baseline
+   * - object: custom SVGO config, used in place of the baseline. To extend
+   *   the baseline, copy `baselineSvgoConfig.plugins` into it.
    */
   svgo?: boolean | SvgoConfig;
 
diff --git a/plugin/src/index.ts b/plugin/src/index.ts
index 65fa940..5bf66ce 100644
--- a/plugin/src/index.ts
+++ b/plugin/src/index.ts
@@ -77,3 +77,4 @@ export const SvgJarPlugin: UnpluginInstance<SvgJarOptions | undefined, false> =
 });
 
 export type { SvgJarOptions, SvgJarTarget } from './core/options.ts';
+export { baselineSvgoConfig } from './svg/optimize.ts';
diff --git a/plugin/src/svg/optimize.ts b/plugin/src/svg/optimize.ts
index 4ebf9fc..abe31e7 100644
--- a/plugin/src/svg/optimize.ts
+++ b/plugin/src/svg/optimize.ts
@@ -1,15 +1,30 @@
-import { optimize, type Config as SvgoConfig } from 'svgo';
+import { optimize, type Config as SvgoConfig, type PluginConfig } from 'svgo';
 
 export type { Config as SvgoConfig } from 'svgo';
 
+/** Freezes an object and every object inside it. */
+function deepFreeze<T extends object>(value: T): T {
+  for (const child of Object.values(value)) {
+    if (typeof child === 'object' && child !== null) deepFreeze(child);
+  }
+  return Object.freeze(value);
+}
+
 /**
  * Baseline SVGO configuration used when `svgo: true` (the default).
  *
  * Preserves IDs (needed for sprite symbol references), path data
  * precision, numeric values, and hidden elements. Strips `<title>`
  * elements since they cause tooltip issues in browsers.
+ *
+ * A custom `svgo` config replaces this one. To extend it, copy its plugins
+ * into the custom config. It is frozen so that changes made by one caller
+ * cannot change the default for every build.
+ *
+ * @example
+ *   svgJar({ svgo: { plugins: [...baselineSvgoConfig.plugins, 'removeDimensions'] } })
  */
-const BASELINE_CONFIG: SvgoConfig = {
+export const baselineSvgoConfig: { readonly plugins: readonly PluginConfig[] } = deepFreeze({
   plugins: [
     {
       name: 'preset-default',
@@ -24,14 +39,14 @@ const BASELINE_CONFIG: SvgoConfig = {
     },
     'removeTitle',
   ],
-};
+});
 
 /**
  * Optimizes an SVG string using SVGO.
  *
  * @param svg    The raw SVG string to optimize.
  * @param config Controls optimization behavior:
- *               - `true`:  use baseline config (default)
+ *               - `true`:  use `baselineSvgoConfig` (default)
  *               - `false`: return the SVG unchanged
  *               - object:  custom SVGO config (used as-is, not merged)
  * @returns The optimized SVG string.
@@ -46,7 +61,7 @@ export function optimizeSvg(svg: string, config: boolean | SvgoConfig): string {
     return svg;
   }
 
-  const svgoConfig = config === true ? BASELINE_CONFIG : config;
+  const svgoConfig = config === true ? { plugins: [...baselineSvgoConfig.plugins] } : config;
   const result = optimize(svg, svgoConfig);
   return result.data;
 }
diff --git a/plugin/test/unit/optimize.test.ts b/plugin/test/unit/optimize.test.ts
index 53e23e7..c8701d6 100644
--- a/plugin/test/unit/optimize.test.ts
+++ b/plugin/test/unit/optimize.test.ts
@@ -2,6 +2,7 @@ import { readFileSync } from 'node:fs';
 import path from 'node:path';
 import { describe, it, expect } from 'vitest';
 import { optimizeSvg } from '../../src/svg/optimize.ts';
+import { baselineSvgoConfig } from '../../src/index.ts';
 
 const FIXTURES_DIR = path.join(import.meta.dirname, '..', '_fixtures');
 
@@ -71,6 +72,34 @@ describe('optimizeSvg', () => {
     });
   });
 
+  describe('baselineSvgoConfig', () => {
+    it('is the config used when svgo is true', () => {
+      const input = readFixture('source-order.svg');
+
+      expect(optimizeSvg(input, { plugins: [...baselineSvgoConfig.plugins] })).toBe(optimizeSvg(input, true));
+    });
+
+    it('can be extended with more plugins', () => {
+      const input = readFixture('with-dimensions.svg');
+      const output = optimizeSvg(input, { plugins: [...baselineSvgoConfig.plugins, 'removeDimensions'] });
+
+      // removeDimensions ran
+      expect(output).not.toContain('width="24"');
+      // The baseline cleanupIds settings still apply
+      expect(optimizeSvg(readFixture('nested-groups.svg'), { plugins: [...baselineSvgoConfig.plugins] })).toContain(
+        'id="outer"',
+      );
+    });
+
+    it('cannot be changed by the caller', () => {
+      expect(Object.isFrozen(baselineSvgoConfig)).toBe(true);
+      expect(Object.isFrozen(baselineSvgoConfig.plugins)).toBe(true);
+      expect(() => {
+        (baselineSvgoConfig.plugins as unknown[]).push('removeDimensions');
+      }).toThrow(TypeError);
+    });
+  });
+
   describe('with custom config', () => {
     it('applies the custom SVGO config', () => {
       const input =
@@ -82,5 +111,14 @@ describe('optimizeSvg', () => {
       expect(output).not.toContain('<!-- comment -->');
       expect(output).toContain('<path');
     });
+
+    it('uses the custom config in place of the baseline, without merging', () => {
+      const input =
+        '<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><title>My Icon</title><path d="M0 0"/></svg>';
+      const output = optimizeSvg(input, { plugins: ['removeComments'] });
+
+      // The baseline removes <title>, so its presence shows the baseline did not run
+      expect(output).toContain('<title>My Icon</title>');
+    });
   });
 });