diff --git a/tools/isobuild/import-scanner.js b/tools/isobuild/import-scanner.js
index a259c30295..0ee4683f15 100644
--- a/tools/isobuild/import-scanner.js
+++ b/tools/isobuild/import-scanner.js
@@ -121,7 +121,8 @@ export default class ImportScanner {
   }
 
   getOutputFiles(options) {
-    return this.outputFiles;
+    // Return all installable output files.
+    return this.outputFiles.filter(file => !! file.installPath);
   }
 
   _findImportedModuleIdentifiers(file) {
diff --git a/tools/isobuild/package-source.js b/tools/isobuild/package-source.js
index fd0a0ae283..2652a16353 100644
--- a/tools/isobuild/package-source.js
+++ b/tools/isobuild/package-source.js
@@ -1316,6 +1316,16 @@ _.extend(PackageSource.prototype, {
     const fileOptions = {};
     const dirs = files.pathDirname(relPath).split(files.pathSep);
 
+    // If the file is restricted to the opposite architecture, make sure
+    // it is not evaluated eagerly.
+    if (arch === "os") {
+      if (dirs.indexOf("client") >= 0) {
+        fileOptions.lazy = true;
+      }
+    } else if (dirs.indexOf("server") >= 0) {
+      fileOptions.lazy = true;
+    }
+
     if (dirs.indexOf("node_modules") >= 0) {
       fileOptions.lazy = true;
       fileOptions.transpile = false;
@@ -1373,7 +1383,6 @@ _.extend(PackageSource.prototype, {
     const anyLevelExcludes = [
       /^tests\/$/,
       /^node_modules\/$/,
-      arch === "os" ? /^client\/$/ : /^server\/$/,
       ...sourceReadOptions.exclude
     ];
 
diff --git a/tools/tests/apps/modules/client/eager.js b/tools/tests/apps/modules/client/eager.js
new file mode 100644
index 0000000000..f3e9aa9c6f
--- /dev/null
+++ b/tools/tests/apps/modules/client/eager.js
@@ -0,0 +1 @@
+export const name = module.id;
diff --git a/tools/tests/apps/modules/tests.js b/tools/tests/apps/modules/tests.js
index 5feb891315..91447b64a6 100644
--- a/tools/tests/apps/modules/tests.js
+++ b/tools/tests/apps/modules/tests.js
@@ -5,6 +5,12 @@ import {Meteor as ImportedMeteor} from "meteor/meteor";
 describe("app modules", () => {
   it("can be imported using absolute identifiers", () => {
     assert.strictEqual(require("/tests"), exports);
+    assert.strictEqual(
+      // Client modules should be importable by server modules, though not
+      // vice-versa.
+      require("/client/eager").name,
+      "/client/eager.js"
+    );
   });
 
   it("can have different file extensions", () => {