diff --git a/src/ast.rs b/src/ast.rs
index ebf38250..4a31d1f9 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -83,6 +83,10 @@ impl FnAccess {
 /// This type is volatile and may change.
 #[derive(Debug, Clone)]
 pub struct ScriptFnDef {
+    /// Function body.
+    pub body: Stmt,
+    /// Encapsulated running environment, if any.
+    pub lib: Option<Shared<Module>>,
     /// Function name.
     pub name: ImmutableString,
     /// Function access mode.
@@ -92,12 +96,6 @@ pub struct ScriptFnDef {
     /// Access to external variables.
     #[cfg(not(feature = "no_closure"))]
     pub externals: HashSet<String>,
-    /// Function body.
-    pub body: Stmt,
-    /// Position of the function definition.
-    pub pos: Position,
-    /// Encapsulated running environment, if any.
-    pub lib: Option<Shared<Module>>,
 }
 
 impl fmt::Display for ScriptFnDef {
@@ -1240,3 +1238,19 @@ impl Expr {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// This test is to make sure no code changes increase the sizes of critical data structures.
+    #[test]
+    fn check_struct_sizes() {
+        use std::mem::size_of;
+
+        assert_eq!(size_of::<Dynamic>(), 16);
+        assert_eq!(size_of::<Option<Dynamic>>(), 16);
+        assert_eq!(size_of::<Expr>(), 16);
+        assert_eq!(size_of::<Stmt>(), 32);
+    }
+}
diff --git a/src/optimize.rs b/src/optimize.rs
index 3778a7b1..e549fc8b 100644
--- a/src/optimize.rs
+++ b/src/optimize.rs
@@ -866,7 +866,6 @@ pub fn optimize_into_ast(
                         params: fn_def.params.clone(),
                         #[cfg(not(feature = "no_closure"))]
                         externals: fn_def.externals.clone(),
-                        pos: fn_def.pos,
                         lib: None,
                     }
                     .into()
diff --git a/src/parser.rs b/src/parser.rs
index d808522e..448df46f 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -2485,7 +2485,6 @@ fn parse_fn(
         #[cfg(not(feature = "no_closure"))]
         externals,
         body,
-        pos: settings.pos,
         lib: None,
     })
 }
@@ -2655,7 +2654,6 @@ fn parse_anon_fn(
         #[cfg(not(feature = "no_closure"))]
         externals: Default::default(),
         body,
-        pos: settings.pos,
         lib: None,
     };