diff --git a/gitbuildrecipe/recipe.py b/gitbuildrecipe/recipe.py
index 0ff215f..9540704 100644
--- a/gitbuildrecipe/recipe.py
+++ b/gitbuildrecipe/recipe.py
@@ -318,6 +318,8 @@ def pull_or_clone(base_branch, target_path):
         # checkout to interpret its argument as a commit?), but that's
         # their problem.
         base_branch.git_call("checkout", base_branch.commit)
+        # initialize submodules
+        base_branch.git_call("submodule", "update", "--init", "--recursive")
     except subprocess.CalledProcessError as e:
         raise CheckoutFailed(e.output)