diff --git a/src/build.ts b/src/build.ts
index b8e3c3645..10fb8d063 100644
--- a/src/build.ts
+++ b/src/build.ts
@@ -121,11 +121,11 @@ export async function build(
         effects.output.write(`${faint("build")} ${specifier} ${faint("→")} `);
         if (specifier.startsWith("observablehq:theme-")) {
           const match = /^observablehq:theme-(?<theme>[\w-]+(,[\w-]+)*)?\.css$/.exec(specifier);
-          const contents = await bundleStyles({theme: match!.groups!.theme?.split(",") ?? []});
+          const contents = await bundleStyles({theme: match!.groups!.theme?.split(",") ?? [], minify: true});
           await effects.writeFile(path, contents);
         } else {
           const clientPath = getClientPath(path.slice("/_observablehq/".length));
-          const contents = await bundleStyles({path: clientPath});
+          const contents = await bundleStyles({path: clientPath, minify: true});
           await effects.writeFile(`/_observablehq/${specifier.slice("observablehq:".length)}`, contents);
         }
       } else if (specifier.startsWith("npm:")) {
@@ -136,7 +136,7 @@ export async function build(
       } else if (!/^\w+:/.test(specifier)) {
         const sourcePath = join(root, specifier);
         effects.output.write(`${faint("build")} ${sourcePath} ${faint("→")} `);
-        const contents = await bundleStyles({path: sourcePath});
+        const contents = await bundleStyles({path: sourcePath, minify: true});
         const hash = createHash("sha256").update(contents).digest("hex").slice(0, 8);
         const ext = extname(specifier);
         const alias = `/${join("_import", dirname(specifier), `${basename(specifier, ext)}.${hash}${ext}`)}`;
diff --git a/src/rollup.ts b/src/rollup.ts
index 504452e9b..e0d42a604 100644
--- a/src/rollup.ts
+++ b/src/rollup.ts
@@ -33,11 +33,20 @@ function rewriteInputsNamespace(code: string) {
   return code.replace(/\b__ns__\b/g, "inputs-3a86ea");
 }
 
-export async function bundleStyles({path, theme}: {path?: string; theme?: string[]}): Promise<string> {
+export async function bundleStyles({
+  minify = false,
+  path,
+  theme
+}: {
+  minify?: boolean;
+  path?: string;
+  theme?: string[];
+}): Promise<string> {
   const result = await build({
     bundle: true,
     ...(path ? {entryPoints: [path]} : {stdin: {contents: renderTheme(theme!), loader: "css"}}),
     write: false,
+    minify,
     alias: STYLE_MODULES
   });
   const text = result.outputFiles[0].text;