diff --git a/source/build.ts b/source/build.ts
index 5072881..d3259fd 100644
--- a/source/build.ts
+++ b/source/build.ts
@@ -34,9 +34,9 @@ const test = process.env.TEST === "true";
 const watch = process.env.WATCH === "true";
 
 // Create absolute paths to various directories.
-const buildDir = toAbsolutePath("build");
+const buildDir = toAbsolutePath("../build");
 const outDir = path.join(buildDir, browser);
-const sourceDir = toAbsolutePath("source");
+const sourceDir = toAbsolutePath("../source");
 
 // Ensure that the output directory exists.
 await fsp.mkdir(outDir, {recursive: true});