diff --git a/__tests__/__datasets__/security-root-level.json b/__tests__/__datasets__/security-root-level.json
new file mode 100644
index 00000000..1dab26b2
--- /dev/null
+++ b/__tests__/__datasets__/security-root-level.json
@@ -0,0 +1,60 @@
+{
+  "openapi": "3.0.3",
+  "info": {
+    "version": "1.0.0",
+    "title": "Example API definition with a root-defined `security` setup."
+  },
+  "servers": [
+    {
+      "url": "https://httpbin.org"
+    }
+  ],
+  "security": [
+    {
+      "apiKey_query": []
+    }
+  ],
+  "paths": {
+    "/anything/apiKey": {
+      "get": {
+        "summary": "Query parameter",
+        "description": "`apiKey` auth will be supplied within an `apiKey` query parameter.",
+        "responses": {
+          "200": {
+            "description": "OK"
+          }
+        }
+      },
+      "post": {
+        "summary": "Cookie",
+        "description": "`apiKey` auth will be supplied within an `api_key` cookie.",
+        "responses": {
+          "200": {
+            "description": "OK"
+          }
+        },
+        "security": [
+          {
+            "apiKey_cookie": []
+          }
+        ]
+      }
+    }
+  },
+  "components": {
+    "securitySchemes": {
+      "apiKey_cookie": {
+        "type": "apiKey",
+        "in": "cookie",
+        "name": "api_key",
+        "description": "An API key that will be supplied in a named cookie. https://github.com/OAI/OpenAPI-Specification/blob/main/versions/3.0.3.md#security-scheme-object"
+      },
+      "apiKey_query": {
+        "type": "apiKey",
+        "in": "query",
+        "name": "apiKey",
+        "description": "An API key that will be supplied in a named query parameter. https://github.com/OAI/OpenAPI-Specification/blob/main/versions/3.0.3.md#security-scheme-object"
+      }
+    }
+  }
+}
diff --git a/__tests__/lib/reducer.test.ts b/__tests__/lib/reducer.test.ts
index a5a8cc85..1973bccd 100644
--- a/__tests__/lib/reducer.test.ts
+++ b/__tests__/lib/reducer.test.ts
@@ -7,6 +7,7 @@ import { expect, describe, it } from 'vitest';
 import reducer from '../../src/lib/reducer';
 import complexNesting from '../__datasets__/complex-nesting.json';
 import petstoreRefQuirks from '../__datasets__/petstore-ref-quirks.json';
+import securityRootLevel from '../__datasets__/security-root-level.json';
 import tagQuirks from '../__datasets__/tag-quirks.json';
 
 describe('reducer', () => {
@@ -160,6 +161,17 @@ describe('reducer', () => {
     });
   });
 
+  it('should retain securitySchemes for root-level security definitions', () => {
+    const reduced = reducer(securityRootLevel as any, { paths: { '/anything/apiKey': '*' } });
+
+    expect(reduced.components).toStrictEqual({
+      securitySchemes: {
+        apiKey_cookie: expect.any(Object),
+        apiKey_query: expect.any(Object),
+      },
+    });
+  });
+
   it("should not leave any components if there aren't any in use", () => {
     const reduced = reducer(uspto as any, { paths: { '/{dataset}/{version}/records': '*' } });
 
diff --git a/src/lib/reducer.ts b/src/lib/reducer.ts
index fe654fc9..1177e04d 100644
--- a/src/lib/reducer.ts
+++ b/src/lib/reducer.ts
@@ -88,6 +88,15 @@ export default function reducer(definition: OASDocument, opts: ReducerOptions =
   // Stringify and parse so we get a full non-reference clone of the API definition to work with.
   const reduced = JSON.parse(JSON.stringify(definition)) as OASDocument;
 
+  // Retain any root-level security definitions.
+  if ('security' in reduced) {
+    Object.values(reduced.security).forEach(sec => {
+      Object.keys(sec).forEach(scheme => {
+        $refs.add(`#/components/securitySchemes/${scheme}`);
+      });
+    });
+  }
+
   if ('paths' in reduced) {
     Object.keys(reduced.paths).forEach(path => {
       const pathLC = path.toLowerCase();