diff --git a/tests/audit_rebase_invocation.rs b/tests/audit_rebase_invocation.rs
index bb88d78..7db3a0f 100644
--- a/tests/audit_rebase_invocation.rs
+++ b/tests/audit_rebase_invocation.rs
@@ -159,6 +159,7 @@ fn build_f1_scenario(repo: &Repository, path_to_repo: &Path) {
 /// which is git's own form. Half B remains the reference both halves are compared against.
 #[test]
 fn audit_f1_chain_rebase_skips_already_applied_commits() {
+    std::env::set_var("LANG", "C");
     // ---------------------------------------------------------------------------------
     // Half A — git-chain's construction: expected (defectively) to conflict.
     // ---------------------------------------------------------------------------------
diff --git a/tests/prune.rs b/tests/prune.rs
index 037ed5a..33e443d 100644
--- a/tests/prune.rs
+++ b/tests/prune.rs
@@ -211,6 +211,7 @@ fn prune_nonexistent_chain() {
 
 #[test]
 fn rebase_suggests_prune_when_branch_is_ancestor_of_root() {
+    std::env::set_var("LANG", "C");
     let repo_name = "rebase_suggests_prune_when_branch_is_ancestor_of_root";
     let repo = setup_git_repo(repo_name);
     let path_to_repo = generate_path_to_repo(repo_name);
@@ -423,6 +424,7 @@ fn rebase_suggests_prune_when_branch_is_ancestor_of_root() {
 
 #[test]
 fn rebase_does_not_suggest_prune_when_no_ancestor() {
+    std::env::set_var("LANG", "C");
     let repo_name = "rebase_does_not_suggest_prune_when_no_ancestor";
     let repo = setup_git_repo(repo_name);
     let path_to_repo = generate_path_to_repo(repo_name);