diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 1ca6b45..09cf548 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -16,7 +16,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, macos-latest]
+        os: [ubuntu-latest, macos-latest, windows-latest]
         runtime: ['node', 'bun', 'deno']
         node-version: [20.x]
     
diff --git a/examples/windows-fetch-workaround/test-with-polyfill.mjs b/examples/windows-fetch-workaround/test-with-polyfill.mjs
new file mode 100755
index 0000000..461f197
--- /dev/null
+++ b/examples/windows-fetch-workaround/test-with-polyfill.mjs
@@ -0,0 +1,36 @@
+#!/usr/bin/env node
+
+/**
+ * Example: Using use-m on Windows with fetch polyfill
+ *
+ * This demonstrates the workaround for issue #45 where fetch is not defined
+ * in certain Windows contexts (Git Bash, shebang execution).
+ *
+ * Solution: Import the fetch-polyfill before loading use-m
+ */
+
+console.log('Platform:', process.platform);
+console.log('Node version:', process.version);
+console.log('Fetch available initially:', typeof fetch !== 'undefined');
+
+// Import fetch polyfill to ensure fetch is available
+// This handles the Windows Git Bash issue where fetch isn't in global scope
+await import('../../fetch-polyfill.js');
+
+console.log('Fetch available after polyfill:', typeof fetch !== 'undefined');
+
+// Now load use-m as usual
+const { use } = eval(
+  await (
+    await fetch('https://unpkg.com/use-m/use.js')
+  ).text()
+);
+
+console.log('\n✅ Successfully loaded use-m');
+
+// Test with lodash
+const _ = await use('lodash@4.17.21');
+console.log('✅ Successfully loaded lodash');
+console.log('Test: _.add(1, 2) =', _.add(1, 2));
+
+console.log('\n🎉 All tests passed!');
diff --git a/examples/windows-fetch-workaround/test-without-polyfill.mjs b/examples/windows-fetch-workaround/test-without-polyfill.mjs
new file mode 100755
index 0000000..dfd334a
--- /dev/null
+++ b/examples/windows-fetch-workaround/test-without-polyfill.mjs
@@ -0,0 +1,38 @@
+#!/usr/bin/env node
+
+/**
+ * Example: Testing fetch availability without polyfill
+ *
+ * This script reproduces issue #45 by attempting to use fetch without
+ * ensuring it's available first.
+ */
+
+console.log('Platform:', process.platform);
+console.log('Node version:', process.version);
+console.log('Fetch available:', typeof fetch !== 'undefined');
+
+if (typeof fetch === 'undefined') {
+  console.error('\n❌ ERROR: fetch is not defined!');
+  console.error('\nThis is the issue described in #45.');
+  console.error('To fix this, use the fetch polyfill:');
+  console.error('  await import("use-m/fetch-polyfill.js");');
+  console.error('\nOr see: examples/windows-fetch-workaround/test-with-polyfill.mjs');
+  process.exit(1);
+}
+
+// Attempt to load use-m
+try {
+  const { use } = eval(
+    await (
+      await fetch('https://unpkg.com/use-m/use.js')
+    ).text()
+  );
+
+  console.log('✅ Successfully loaded use-m');
+
+  const _ = await use('lodash@4.17.21');
+  console.log('✅ Test passed: _.add(1, 2) =', _.add(1, 2));
+} catch (error) {
+  console.error('❌ Failed:', error.message);
+  process.exit(1);
+}
diff --git a/experiments/test-fetch-availability.mjs b/experiments/test-fetch-availability.mjs
new file mode 100755
index 0000000..becb282
--- /dev/null
+++ b/experiments/test-fetch-availability.mjs
@@ -0,0 +1,42 @@
+#!/usr/bin/env node
+
+/**
+ * Test script to reproduce issue #45: fetch is not defined on Windows
+ *
+ * This script checks:
+ * 1. Node.js version
+ * 2. Whether fetch is available
+ * 3. Whether we can load use-m with fetch
+ */
+
+console.log('=== Fetch Availability Test ===');
+console.log('Node version:', process.version);
+console.log('Platform:', process.platform);
+console.log('Fetch available:', typeof fetch !== 'undefined');
+console.log('Global fetch:', typeof globalThis.fetch !== 'undefined');
+
+// Test if fetch works
+if (typeof fetch === 'undefined') {
+  console.error('\n❌ ERROR: fetch is not defined!');
+  console.log('\nThis is the bug described in issue #45');
+  console.log('Expected: fetch should be available in Node.js 18+');
+  console.log('Actual: fetch is undefined');
+  process.exit(1);
+} else {
+  console.log('\n✅ fetch is available');
+
+  // Try to load use-m
+  try {
+    console.log('\nTrying to load use-m...');
+    const { use } = eval(await (await fetch('https://unpkg.com/use-m/use.js')).text());
+    console.log('✅ Successfully loaded use-m');
+
+    // Test using a package
+    const _ = await use('lodash@4.17.21');
+    console.log('✅ Successfully loaded lodash via use-m');
+    console.log('Test: _.add(1, 2) =', _.add(1, 2));
+  } catch (error) {
+    console.error('❌ Failed to load use-m:', error.message);
+    process.exit(1);
+  }
+}
diff --git a/experiments/test-fetch-polyfill.mjs b/experiments/test-fetch-polyfill.mjs
new file mode 100644
index 0000000..631c8f6
--- /dev/null
+++ b/experiments/test-fetch-polyfill.mjs
@@ -0,0 +1,101 @@
+#!/usr/bin/env node
+
+/**
+ * Test script demonstrating fetch polyfill for issue #45
+ *
+ * This shows how to ensure fetch is available before loading use-m
+ */
+
+console.log('=== Testing fetch polyfill approach ===');
+console.log('Node version:', process.version);
+console.log('Platform:', process.platform);
+console.log('Initial fetch available:', typeof fetch !== 'undefined');
+
+// Polyfill fetch if not available (for Node.js 18+ with Windows Git Bash issues)
+if (typeof fetch === 'undefined') {
+  console.log('\n⚠️  fetch is not defined, attempting to use node:http/https as fallback...');
+
+  // For Node.js 18+, fetch should be available but might not be in certain contexts
+  // We can try to explicitly import it from node:
+  try {
+    // Try to import fetch from Node.js built-ins (Node 18+)
+    // This is a workaround for contexts where global fetch isn't initialized
+    const { default: nodeFetch } = await import('node:http').then(() => {
+      // Actually try to get fetch from the global after a tick
+      return new Promise(resolve => {
+        setImmediate(() => {
+          if (typeof fetch !== 'undefined') {
+            resolve({ default: fetch });
+          } else {
+            throw new Error('fetch still not available');
+          }
+        });
+      });
+    }).catch(async () => {
+      // If Node.js built-in fetch is not available, fall back to https module
+      const https = await import('node:https');
+      const http = await import('node:http');
+
+      return {
+        default: (url, options = {}) => {
+          return new Promise((resolve, reject) => {
+            const parsedUrl = new URL(url);
+            const protocol = parsedUrl.protocol === 'https:' ? https : http;
+
+            const req = protocol.request(parsedUrl, {
+              method: options.method || 'GET',
+              headers: options.headers || {},
+            }, (res) => {
+              let data = '';
+              res.on('data', chunk => data += chunk);
+              res.on('end', () => {
+                resolve({
+                  ok: res.statusCode >= 200 && res.statusCode < 300,
+                  status: res.statusCode,
+                  statusText: res.statusMessage,
+                  headers: res.headers,
+                  text: () => Promise.resolve(data),
+                  json: () => Promise.resolve(JSON.parse(data)),
+                });
+              });
+            });
+
+            req.on('error', reject);
+
+            if (options.body) {
+              req.write(options.body);
+            }
+
+            req.end();
+          });
+        }
+      };
+    });
+
+    globalThis.fetch = nodeFetch;
+    console.log('✅ fetch polyfill installed');
+  } catch (error) {
+    console.error('❌ Failed to install fetch polyfill:', error.message);
+    process.exit(1);
+  }
+}
+
+console.log('Final fetch available:', typeof fetch !== 'undefined');
+
+// Now try to load use-m
+try {
+  console.log('\nLoading use-m...');
+  const { use } = eval(await (await fetch('https://unpkg.com/use-m/use.js')).text());
+  console.log('✅ Successfully loaded use-m');
+
+  // Test using a package
+  const _ = await use('lodash@4.17.21');
+  console.log('✅ Successfully loaded lodash via use-m');
+  console.log('Test: _.add(1, 2) =', _.add(1, 2));
+
+  console.log('\n✅ All tests passed!');
+} catch (error) {
+  console.error('❌ Failed:', error.message);
+  console.error(error.stack);
+  process.exit(1);
+}
diff --git a/experiments/test-polyfill-no-fetch.mjs b/experiments/test-polyfill-no-fetch.mjs
new file mode 100755
index 0000000..a00ceca
--- /dev/null
+++ b/experiments/test-polyfill-no-fetch.mjs
@@ -0,0 +1,55 @@
+#!/usr/bin/env node
+
+/**
+ * Test the fetch polyfill by simulating a scenario where fetch is not available
+ */
+
+console.log('=== Testing fetch polyfill with simulated missing fetch ===');
+console.log('Node version:', process.version);
+console.log('Platform:', process.platform);
+console.log('Fetch initially available:', typeof fetch !== 'undefined');
+
+// Simulate the Windows Git Bash issue by removing fetch from global scope
+const originalFetch = globalThis.fetch;
+delete globalThis.fetch;
+
+console.log('Fetch after deletion:', typeof fetch !== 'undefined');
+
+// Now import the polyfill
+try {
+  await import('../fetch-polyfill.js');
+  console.log('✅ Polyfill imported successfully');
+  console.log('Fetch after polyfill:', typeof fetch !== 'undefined');
+
+  if (typeof fetch === 'undefined') {
+    console.error('❌ Polyfill failed to install fetch');
+    process.exit(1);
+  }
+
+  // Test that fetch works
+  console.log('\nTesting fetch...');
+  const response = await fetch('https://unpkg.com/use-m/package.json');
+  const data = await response.json();
+  console.log('✅ Fetch works! Package name:', data.name);
+
+  // Now test loading use-m
+  console.log('\nTesting use-m...');
+  const { use } = eval(await (await fetch('https://unpkg.com/use-m/use.js')).text());
+  console.log('✅ use-m loaded successfully');
+
+  const _ = await use('lodash@4.17.21');
+  console.log('✅ lodash loaded successfully');
+  console.log('Test: _.add(1, 2) =', _.add(1, 2));
+
+  console.log('\n🎉 All tests passed!');
+} catch (error) {
+  console.error('❌ Test failed:', error.message);
+  console.error(error.stack);
+
+  // Restore original fetch
+  if (originalFetch) {
+    globalThis.fetch = originalFetch;
+  }
+
+  process.exit(1);
+}
diff --git a/fetch-polyfill.js b/fetch-polyfill.js
new file mode 100644
index 0000000..db418ba
--- /dev/null
+++ b/fetch-polyfill.js
@@ -0,0 +1,108 @@
+/**
+ * Fetch polyfill for Node.js environments where fetch is not available
+ *
+ * This addresses issue #45 where fetch is not defined in certain Windows contexts
+ * (e.g., Git Bash, shebang execution) even in Node.js 18+.
+ *
+ * Usage:
+ *   // Ensure fetch is available before loading use-m
+ *   await import('use-m/fetch-polyfill.js');
+ *   const { use } = eval(await (await fetch('https://unpkg.com/use-m/use.js')).text());
+ *
+ * Or with a local import:
+ *   await import('./fetch-polyfill.js');
+ */
+
+// Only install polyfill if fetch is not already available
+const needsPolyfill = typeof globalThis !== 'undefined' && typeof globalThis.fetch === 'undefined';
+
+if (needsPolyfill) {
+  // Create a minimal fetch implementation using node:http/https
+  const installPolyfill = async () => {
+    try {
+      // First, try to import from undici (Node.js 18+)
+      let fetchImpl;
+
+      try {
+        const undici = await import('undici');
+        fetchImpl = undici.fetch;
+      } catch {
+        // If undici is not available, create a minimal fetch using node:http/https
+        const https = await import('node:https');
+        const http = await import('node:http');
+        const { URL } = await import('node:url');
+
+        fetchImpl = (url, options = {}, redirectCount = 0) => {
+          const MAX_REDIRECTS = 20;
+
+          return new Promise((resolve, reject) => {
+            const parsedUrl = new URL(url);
+            const protocol = parsedUrl.protocol === 'https:' ? https : http;
+
+            const requestOptions = {
+              method: options.method || 'GET',
+              headers: options.headers || {},
+            };
+
+            const req = protocol.request(parsedUrl, requestOptions, (res) => {
+              // Handle redirects (301, 302, 303, 307, 308)
+              if (res.statusCode >= 300 && res.statusCode < 400 && res.headers.location) {
+                if (redirectCount >= MAX_REDIRECTS) {
+                  return reject(new Error('Too many redirects'));
+                }
+
+                const redirectUrl = new URL(res.headers.location, url).href;
+                return resolve(fetchImpl(redirectUrl, options, redirectCount + 1));
+              }
+
+              const chunks = [];
+
+              res.on('data', chunk => chunks.push(chunk));
+
+              res.on('end', () => {
+                const buffer = Buffer.concat(chunks);
+                const text = buffer.toString('utf-8');
+
+                resolve({
+                  ok: res.statusCode >= 200 && res.statusCode < 300,
+                  status: res.statusCode,
+                  statusText: res.statusMessage,
+                  headers: res.headers,
+                  url: url,
+                  redirected: redirectCount > 0,
+                  type: 'basic',
+                  text: () => Promise.resolve(text),
+                  json: () => Promise.resolve(JSON.parse(text)),
+                  blob: () => Promise.resolve(buffer),
+                  arrayBuffer: () => Promise.resolve(buffer.buffer.slice(buffer.byteOffset, buffer.byteOffset + buffer.byteLength)),
+                });
+              });
+            });
+
+            req.on('error', reject);
+
+            if (options.body) {
+              req.write(options.body);
+            }
+
+            req.end();
+          });
+        };
+      }
+
+      // Install fetch polyfill globally
+      globalThis.fetch = fetchImpl;
+    } catch (error) {
+      // If polyfill installation fails, provide a helpful error message
+      console.error('Failed to install fetch polyfill:', error.message);
+      console.error('Please ensure you are running Node.js 18+ or install node-fetch manually.');
+    }
+  };
+
+  // Execute the polyfill installation
+  await installPolyfill();
+}
+
+// Export the fetch function (either native or polyfilled)
+export const fetch = globalThis.fetch;
+export default globalThis.fetch;
diff --git a/package.json b/package.json
index 545fac8..a69e854 100644
--- a/package.json
+++ b/package.json
@@ -10,7 +10,8 @@
       "require": "./use.cjs"
     },
     "./use.cjs": "./use.cjs",
-    "./use.mjs": "./use.mjs"
+    "./use.mjs": "./use.mjs",
+    "./fetch-polyfill.js": "./fetch-polyfill.js"
   },
   "bin": {
     "use": "./cli.mjs"