diff --git a/.changeset/mean-lands-pull.md b/.changeset/mean-lands-pull.md
new file mode 100644
index 000000000000..8e6e47d76270
--- /dev/null
+++ b/.changeset/mean-lands-pull.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fixes a case where font sources with relative protocol URLs would fail when using the experimental fonts API
diff --git a/packages/astro/src/assets/fonts/logic/normalize-remote-font-faces.ts b/packages/astro/src/assets/fonts/logic/normalize-remote-font-faces.ts
index c4689f0f77cd..80288feaa310 100644
--- a/packages/astro/src/assets/fonts/logic/normalize-remote-font-faces.ts
+++ b/packages/astro/src/assets/fonts/logic/normalize-remote-font-faces.ts
@@ -23,11 +23,14 @@ export function normalizeRemoteFontFaces({
 						if ('name' in source) {
 							return source;
 						}
+						// We handle protocol relative URLs here, otherwise they're considered absolute by the font
+						// fetcher which will try to read them from the file system
+						const url = source.url.startsWith('//') ? `https:${source.url}` : source.url;
 						const proxied = {
 							...source,
-							originalURL: source.url,
+							originalURL: url,
 							url: urlProxy.proxy({
-								url: source.url,
+								url,
 								// We only collect the first URL to avoid preloading fallback sources (eg. we only
 								// preload woff2 if woff is available)
 								collectPreload: index === 0,
diff --git a/packages/astro/test/units/assets/fonts/logic.test.js b/packages/astro/test/units/assets/fonts/logic.test.js
index 0fe637868bac..c99a1598efae 100644
--- a/packages/astro/test/units/assets/fonts/logic.test.js
+++ b/packages/astro/test/units/assets/fonts/logic.test.js
@@ -450,6 +450,54 @@ describe('fonts logic', () => {
 				},
 			]);
 		});
+
+		it('turns relative protocols into https', () => {
+			const { collected, urlProxy } = createSpyUrlProxy();
+			const fonts = normalizeRemoteFontFaces({
+				urlProxy,
+				fonts: [
+					{
+						weight: '400',
+						style: 'normal',
+						src: [{ url: '//example.com/font.woff2' }, { url: 'http://example.com/font.woff' }],
+					},
+				],
+			});
+
+			assert.deepStrictEqual(
+				fonts,
+				[
+					{
+						src: [
+							{
+								originalURL: 'https://example.com/font.woff2',
+								url: 'https://example.com/font.woff2',
+							},
+							{
+								originalURL: 'http://example.com/font.woff',
+								url: 'http://example.com/font.woff',
+							},
+						],
+						style: 'normal',
+						weight: '400',
+					},
+				],
+			);
+			assert.deepStrictEqual(collected, [
+				{
+					url: 'https://example.com/font.woff2',
+					collectPreload: true,
+					data: { weight: '400', style: 'normal' },
+					init: null,
+				},
+				{
+					url: 'http://example.com/font.woff',
+					collectPreload: false,
+					data: { weight: '400', style: 'normal' },
+					init: null,
+				},
+			]);
+		});
 	});
 
 	describe('optimizeFallbacks()', () => {