diff --git a/cli/src/main.rs b/cli/src/main.rs
index 36b93c5..d19e20b 100644
--- a/cli/src/main.rs
+++ b/cli/src/main.rs
@@ -122,7 +122,9 @@ fn main() -> io::Result<()> {
 
     let settings = {
         let mut settings = if let Some(path) = opt.settings {
-            serde_json::from_reader(File::open(path)?)?
+            let defaults = serde_json::to_value(Settings::default()).unwrap();
+            let overrides = serde_json::from_reader(File::open(path)?)?;
+            serde_json::from_value(merge(defaults, overrides))?
         } else {
             Settings::default()
         };
@@ -384,3 +386,16 @@ fn main() -> io::Result<()> {
         )
     }
 }
+
+fn merge(defaults: serde_json::Value, overrides: serde_json::Value) -> serde_json::Value {
+    match (defaults, overrides) {
+        (serde_json::Value::Object(mut defaults), serde_json::Value::Object(overrides)) => {
+            for (k, v) in overrides {
+                let existing = defaults.remove(&k).unwrap_or(serde_json::Value::Null);
+                defaults.insert(k, merge(existing, v));
+            }
+            serde_json::Value::Object(defaults)
+        }
+        (_, overrides) => overrides,
+    }
+}