diff --git a/internal/job/checkout.go b/internal/job/checkout.go
index 40fdadd6e1..dcbabc7c94 100644
--- a/internal/job/checkout.go
+++ b/internal/job/checkout.go
@@ -600,6 +600,7 @@ func (e *Executor) defaultCheckoutPhase(ctx context.Context) error {
 			e.shell.Warningf("Failed to enumerate git submodules: %v", err)
 		} else {
 			mirrorSubmodules := e.ExecutorConfig.GitMirrorsPath != ""
+			submoduleMirrorDirs := make([]string, 0)
 			for _, repository := range submoduleRepos {
 				submoduleArgs := append([]string(nil), args...)
 				// submodules might need their fingerprints verified too
@@ -617,6 +618,8 @@ func (e *Executor) defaultCheckoutPhase(ctx context.Context) error {
 					return fmt.Errorf("getting/updating mirror dir for submodules: %w", err)
 				}
 
+				submoduleMirrorDirs = append(submoduleMirrorDirs, mirrorDir)
+
 				// Switch back to the checkout dir, doing other operations from GitMirrorsPath will fail.
 				if err := e.createCheckoutDir(); err != nil {
 					return fmt.Errorf("creating checkout dir: %w", err)
@@ -642,6 +645,10 @@ func (e *Executor) defaultCheckoutPhase(ctx context.Context) error {
 				}
 			}
 
+			for i, dir := range submoduleMirrorDirs {
+				e.shell.Env.Set(fmt.Sprintf("BUILDKITE_REPO_SUBMODULE_MIRROR_%d", i), dir)
+			}
+
 			if !mirrorSubmodules {
 				args = append(args, "submodule", "update", "--init", "--recursive", "--force")
 				if err := e.shell.Run(ctx, "git", args...); err != nil {