diff --git a/Cargo.toml b/Cargo.toml
index 7eb97fb9..308685bf 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -19,7 +19,7 @@ num-traits = "*"
 
 [features]
 #default = ["no_function", "no_index", "no_float", "only_i32", "no_stdlib", "unchecked", "no_optimize"]
-default = []
+default = [ "optimize_full" ]
 debug_msgs = []     # print debug messages on function registrations and calls
 unchecked = []      # unchecked arithmetic
 no_stdlib = []      # no standard library of utility functions
@@ -27,6 +27,7 @@ no_index = []       # no arrays and indexing
 no_float = []       # no floating-point
 no_function = []    # no script-defined functions
 no_optimize = []    # no script optimizer
+optimize_full = []  # set optimization level to Full (default is Simple)
 only_i32 = []       # set INT=i32 (useful for 32-bit systems)
 only_i64 = []       # set INT=i64 (default) and disable support for all other integer types
 
diff --git a/src/engine.rs b/src/engine.rs
index 6b951d4e..bee73cff 100644
--- a/src/engine.rs
+++ b/src/engine.rs
@@ -99,14 +99,20 @@ impl Engine<'_> {
 
         // Create the new scripting Engine
         let mut engine = Engine {
-            #[cfg(not(feature = "no_optimize"))]
-            optimization_level: OptimizationLevel::Full,
             ext_functions: HashMap::new(),
             script_functions: Vec::new(),
             type_iterators: HashMap::new(),
             type_names,
             on_print: Box::new(default_print), // default print/debug implementations
             on_debug: Box::new(default_print),
+
+            #[cfg(not(feature = "no_optimize"))]
+            #[cfg(not(feature = "optimize_full"))]
+            optimization_level: OptimizationLevel::Simple,
+
+            #[cfg(not(feature = "no_optimize"))]
+            #[cfg(feature = "optimize_full")]
+            optimization_level: OptimizationLevel::Full,
         };
 
         engine.register_core_lib();