diff --git a/dev/core/src/com/google/gwt/core/ext/linker/impl/StandardLinkerContext.java b/dev/core/src/com/google/gwt/core/ext/linker/impl/StandardLinkerContext.java
index 424fb28..2100ce0 100644
--- a/dev/core/src/com/google/gwt/core/ext/linker/impl/StandardLinkerContext.java
+++ b/dev/core/src/com/google/gwt/core/ext/linker/impl/StandardLinkerContext.java
@@ -171,7 +171,13 @@
     }
 
     // Get the primary linker.
-    sortedLinkers.add(module.getActivePrimaryLinker());
+    Class<? extends Linker> primary = module.getActivePrimaryLinker();
+    if (primary == null) {
+      logger.log(logger.ERROR, "Primary linker is null.  Does your module " +
+          "inherit from com.google.gwt.core.Core or com.google.gwt.user.User?");
+    } else {
+      sortedLinkers.add(module.getActivePrimaryLinker());
+    }
 
     // Get all the post-linkers IN REVERSE ORDER.
     {