diff --git a/src/main/java/com/google/devtools/build/lib/bazel/repository/starlark/StarlarkRepositoryModule.java b/src/main/java/com/google/devtools/build/lib/bazel/repository/starlark/StarlarkRepositoryModule.java
index cf1b9199f6b819..ba95418a06eea5 100644
--- a/src/main/java/com/google/devtools/build/lib/bazel/repository/starlark/StarlarkRepositoryModule.java
+++ b/src/main/java/com/google/devtools/build/lib/bazel/repository/starlark/StarlarkRepositoryModule.java
@@ -220,6 +220,9 @@ private Object createRuleLegacy(StarlarkThread thread, Dict<String, Object> kwar
 
         // TODO(adonovan): is this cast safe? Check.
         String name = (String) kwargs.get("name");
+        if (name == null) {
+          throw Starlark.errorf("argument 'name' is required");
+        }
         WorkspaceFactoryHelper.addMainRepoEntry(packageBuilder, name);
         WorkspaceFactoryHelper.addRepoMappings(packageBuilder, kwargs, name);
         return WorkspaceFactoryHelper.createAndAddRepositoryRule(