diff --git a/esinstall/src/index.ts b/esinstall/src/index.ts
index 8fce8130dc..3e8dde771d 100644
--- a/esinstall/src/index.ts
+++ b/esinstall/src/index.ts
@@ -31,6 +31,7 @@ import {
   createInstallTarget,
   findMatchingAliasEntry,
   getWebDependencyName,
+  isJavaScript,
   isPackageAliasEntry,
   MISSING_PLUGIN_SUGGESTIONS,
   parsePackageImportSpecifier,
@@ -99,9 +100,8 @@ function resolveWebDependency(
     // For details on why we need to call fs.realpathSync.native here and other places, see
     // https://github.com/snowpackjs/snowpack/pull/999.
     const loc = fs.realpathSync.native(require.resolve(dep, {paths: [cwd]}));
-    const isJSFile = ['.js', '.mjs', '.cjs'].includes(path.extname(loc));
     return {
-      type: isJSFile ? 'JS' : 'ASSET',
+      type: isJavaScript(loc) ? 'JS' : 'ASSET',
       loc,
     };
   }
@@ -139,7 +139,7 @@ function resolveWebDependency(
     try {
       const maybeLoc = fs.realpathSync.native(require.resolve(dep, {paths: [cwd]}));
       return {
-        type: 'JS',
+        type: isJavaScript(maybeLoc) ? 'JS' : 'ASSET',
         loc: maybeLoc,
       };
     } catch (err) {
@@ -192,11 +192,12 @@ function resolveWebDependency(
   if (typeof foundEntrypoint !== 'string') {
     throw new Error(`"${dep}" has unexpected entrypoint: ${JSON.stringify(foundEntrypoint)}.`);
   }
+  const loc = fs.realpathSync.native(
+    require.resolve(path.join(depManifestLoc || '', '..', foundEntrypoint)),
+  );
   return {
-    type: 'JS',
-    loc: fs.realpathSync.native(
-      require.resolve(path.join(depManifestLoc || '', '..', foundEntrypoint)),
-    ),
+    type: isJavaScript(loc) ? 'JS' : 'ASSET',
+    loc,
   };
 }
 
diff --git a/esinstall/src/util.ts b/esinstall/src/util.ts
index 6790d25823..2b7676bdb1 100644
--- a/esinstall/src/util.ts
+++ b/esinstall/src/util.ts
@@ -189,3 +189,9 @@ export function createInstallTarget(specifier: string, all = true): InstallTarge
     named: [],
   };
 }
+
+/** Is this file JavaScript?  */
+export function isJavaScript(pathname: string) {
+  const ext = path.extname(pathname).toLowerCase();
+  return ext === '.js' || ext === '.mjs' || ext === '.cjs';
+}