diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4942004e..a09f3801 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,8 @@ Version 1.5.0
 
 This version adds a debugging interface, which can be used to integrate a debugger.
 
+The `REPL` tool uses [`rustyline`](https://crates.io/crates/rustyline) for line editing and history.
+
 Bug fixes
 ---------
 
diff --git a/src/bin/rhai-dbg.rs b/src/bin/rhai-dbg.rs
index 4b289985..263acee4 100644
--- a/src/bin/rhai-dbg.rs
+++ b/src/bin/rhai-dbg.rs
@@ -179,6 +179,9 @@ fn main() {
     // Initialize scripting engine
     let mut engine = Engine::new();
 
+    #[cfg(not(feature = "no_optimize"))]
+    engine.set_optimization_level(rhai::OptimizationLevel::None);
+
     let mut script = String::new();
     let main_ast;