diff --git a/tools/isopack.js b/tools/isopack.js
index 4a5440149c..603feab45c 100644
--- a/tools/isopack.js
+++ b/tools/isopack.js
@@ -132,14 +132,15 @@ _.extend(Unibuild.prototype, {
     // packages get precedence.
     //
     // We don't get imports from unordered dependencies (since they may not be
-    // defined yet) or from weak dependencies (because the meaning of a name
-    // shouldn't be affected by the non-local decision of whether or not an
-    // unrelated package in the target depends on something).
+    // defined yet) or from weak/debugOnly dependencies (because the meaning of
+    // a name shouldn't be affected by the non-local decision of whether or not
+    // an unrelated package in the target depends on something).
     var imports = {}; // map from symbol to supplying package name
     compiler.eachUsedUnibuild(
       self.uses,
       bundleArch, loader,
-      {skipUnordered: true}, function (depUnibuild) {
+      { skipUnordered: true, skipDebugOnly: true },
+      function (depUnibuild) {
         _.each(depUnibuild.packageVariables, function (symbol) {
           // Slightly hacky implementation of test-only exports.
           if (symbol.export === true ||