diff --git a/src/optimizer.rs b/src/optimizer.rs
index 5e19726e..2fcd06bb 100644
--- a/src/optimizer.rs
+++ b/src/optimizer.rs
@@ -1236,6 +1236,16 @@ fn optimize_top_level(
         optimization_level,
     );
 
+    // Add constants from global modules
+    for (name, value) in engine
+        .global_modules
+        .iter()
+        .rev()
+        .flat_map(|m| m.iter_var())
+    {
+        state.push_var(name, AccessMode::ReadOnly, Some(value.clone()));
+    }
+
     // Add constants and variables from the scope
     for (name, constant, value) in scope.iter() {
         if !constant {
diff --git a/tests/optimizer.rs b/tests/optimizer.rs
index 351d91e5..3a203ac2 100644
--- a/tests/optimizer.rs
+++ b/tests/optimizer.rs
@@ -1,6 +1,6 @@
 #![cfg(not(feature = "no_optimize"))]
 
-use rhai::{Engine, EvalAltResult, OptimizationLevel, Scope, INT};
+use rhai::{Engine, EvalAltResult, Module, OptimizationLevel, Scope, INT};
 
 #[test]
 fn test_optimizer() -> Result<(), Box<EvalAltResult>> {
@@ -74,6 +74,7 @@ fn test_optimizer_run() -> Result<(), Box<EvalAltResult>> {
 #[test]
 fn test_optimizer_parse() -> Result<(), Box<EvalAltResult>> {
     let mut engine = Engine::new();
+
     engine.set_optimization_level(OptimizationLevel::Simple);
 
     let ast = engine.compile("{ const DECISION = false; if DECISION { 42 } else { 123 } }")?;
@@ -97,6 +98,22 @@ fn test_optimizer_parse() -> Result<(), Box<EvalAltResult>> {
 
     assert_eq!(format!("{:?}", ast), "AST { body: [Expr(42 @ 1:1)] }");
 
+    let ast = engine.compile("NUMBER")?;
+
+    assert_eq!(
+        format!("{:?}", ast),
+        "AST { body: [Expr(Variable(NUMBER) @ 1:1)] }"
+    );
+
+    let mut module = Module::new();
+    module.set_var("NUMBER", 42 as INT);
+
+    engine.register_global_module(module.into());
+
+    let ast = engine.compile("NUMBER")?;
+
+    assert_eq!(format!("{:?}", ast), "AST { body: [Expr(42 @ 1:1)] }");
+
     Ok(())
 }