diff --git a/src/app/alias.rs b/src/app/alias.rs
index 350c95c67..0f47f5b1e 100644
--- a/src/app/alias.rs
+++ b/src/app/alias.rs
@@ -35,6 +35,11 @@ const DEFAULT_ALIASES_PGP: &str = include_str!("../../assets/ocad.pgp");
 /// config base can't be resolved (headless, no `HOME`).
 #[cfg(not(target_arch = "wasm32"))]
 fn alias_file_path() -> Option<PathBuf> {
+    // Tests read the shipped defaults: parallel tests seeding and migrating one
+    // shared file race, and a half-written table fails unrelated alias tests.
+    if cfg!(test) {
+        return None;
+    }
     Some(crate::config::config_dir()?.join("ocad.pgp"))
 }
 
diff --git a/src/config.rs b/src/config.rs
index e8f907441..6d1e60962 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -10,6 +10,13 @@ use std::path::PathBuf;
 /// file name onto it and `create_dir_all` its parent before writing.
 #[cfg(not(target_arch = "wasm32"))]
 pub fn config_dir() -> Option<PathBuf> {
+    // Tests must never read or write the person's real settings: a test run
+    // once raced dozens of tests through an alias-table migration and left the
+    // user's alias file holding a single line. Every store routes through here,
+    // so one per-process scratch folder isolates them all.
+    if cfg!(test) {
+        return Some(std::env::temp_dir().join(format!("ocs-test-config-{}", std::process::id())));
+    }
     let base: PathBuf = if cfg!(target_os = "windows") {
         std::env::var_os("APPDATA").map(PathBuf::from)?
     } else if cfg!(target_os = "macos") {