diff --git a/internal/pullbox/s3/config.go b/internal/pullbox/s3/config.go
index ff6fdac523a..c8a1004ebc9 100644
--- a/internal/pullbox/s3/config.go
+++ b/internal/pullbox/s3/config.go
@@ -22,23 +22,31 @@ const (
 	region = "us-east-2"
 )
 
-func assumeRole(ctx context.Context, c *devopt.Credentials) (*aws.Config, error) {
-	noPermsConfig, _ := config.LoadDefaultConfig(ctx)
+func assumeRole(ctx context.Context, cred *devopt.Credentials) (*aws.Config, error) {
+	// STS needs an explicit region to resolve its endpoint. Without one,
+	// users who don't have an AWS region configured in their environment hit
+	// "Invalid Configuration: Missing Region" when running `devbox global
+	// push`. Pin it to the bucket's region, same as the config below.
+	noPermsConfig, err := config.LoadDefaultConfig(ctx, config.WithRegion(region))
+	if err != nil {
+		return nil, errors.WithStack(err)
+	}
 	stsClient := sts.NewFromConfig(noPermsConfig)
 	creds, err := stsClient.AssumeRoleWithWebIdentity(
 		ctx,
 		&sts.AssumeRoleWithWebIdentityInput{
 			RoleArn:          aws.String(roleArn),
-			RoleSessionName:  aws.String(c.Email),
-			WebIdentityToken: aws.String(c.IDToken),
+			RoleSessionName:  aws.String(cred.Email),
+			WebIdentityToken: aws.String(cred.IDToken),
 		},
 	)
 	if err != nil {
 		return nil, err
 	}
 
-	config, err := config.LoadDefaultConfig(
+	cfg, err := config.LoadDefaultConfig(
 		ctx,
+		config.WithRegion(region),
 		config.WithCredentialsProvider(
 			credentials.NewStaticCredentialsProvider(
 				*creds.Credentials.AccessKeyId,
@@ -47,9 +55,8 @@ func assumeRole(ctx context.Context, c *devopt.Credentials) (*aws.Config, error)
 			),
 		),
 	)
-	config.Region = region
 	if err != nil {
 		return nil, errors.WithStack(err)
 	}
-	return &config, err
+	return &cfg, nil
 }
diff --git a/internal/pullbox/s3/config_test.go b/internal/pullbox/s3/config_test.go
new file mode 100644
index 00000000000..28faa4c0ee6
--- /dev/null
+++ b/internal/pullbox/s3/config_test.go
@@ -0,0 +1,53 @@
+package s3
+
+import (
+	"testing"
+
+	"github.com/aws/aws-sdk-go-v2/config"
+)
+
+// TestConfigPinsRegion guards against a regression of jetify-com/devbox#2591,
+// where `devbox global push` failed with "Invalid Configuration: Missing
+// Region" for users who had no AWS region configured in their environment.
+//
+// assumeRole builds AWS configs (for both the STS and S3 clients) that must
+// explicitly pin the region, since neither STS nor S3 can resolve an endpoint
+// without one. This test reproduces the reporter's environment (no region
+// configured anywhere) and verifies that pinning the region via
+// config.WithRegion(region) still yields a config with the expected region.
+func TestConfigPinsRegion(t *testing.T) {
+	if region == "" {
+		t.Fatal("region constant must not be empty; STS/S3 endpoint resolution requires it")
+	}
+
+	// Simulate a user with no AWS region configured anywhere: clear the
+	// region environment variables and point the shared config/credentials
+	// files at nonexistent paths so no ambient region leaks in.
+	t.Setenv("AWS_REGION", "")
+	t.Setenv("AWS_DEFAULT_REGION", "")
+	t.Setenv("AWS_CONFIG_FILE", "/dev/null")
+	t.Setenv("AWS_SHARED_CREDENTIALS_FILE", "/dev/null")
+
+	ctx := t.Context()
+
+	// Without an explicit region, the loaded config has no region. This is the
+	// condition that produced the "Missing Region" error before the fix.
+	noRegion, err := config.LoadDefaultConfig(ctx)
+	if err != nil {
+		t.Fatalf("loading default config: %v", err)
+	}
+	if noRegion.Region != "" {
+		t.Skipf("test environment provides a default AWS region (%q); "+
+			"cannot exercise the missing-region case", noRegion.Region)
+	}
+
+	// With the region pinned (as assumeRole now does for both configs), the
+	// region is set regardless of the environment.
+	pinned, err := config.LoadDefaultConfig(ctx, config.WithRegion(region))
+	if err != nil {
+		t.Fatalf("loading config with pinned region: %v", err)
+	}
+	if pinned.Region != region {
+		t.Errorf("pinned region = %q, want %q", pinned.Region, region)
+	}
+}