diff --git a/crates/webidl/src/first_pass.rs b/crates/webidl/src/first_pass.rs
index eeee69ab..02ab48e0 100644
--- a/crates/webidl/src/first_pass.rs
+++ b/crates/webidl/src/first_pass.rs
@@ -22,7 +22,6 @@ use weedle::{DictionaryDefinition, PartialDictionaryDefinition};
 use super::Result;
 use util;
 use util::camel_case_ident;
-use std::cell::RefCell;
 
 /// Collection of constructs that may use partial.
 #[derive(Default)]
@@ -38,7 +37,7 @@ pub(crate) struct FirstPassRecord<'src> {
     pub(crate) dictionaries: BTreeMap<&'src str, DictionaryData<'src>>,
     pub(crate) callbacks: BTreeSet<&'src str>,
     pub(crate) callback_interfaces: BTreeMap<&'src str, CallbackInterfaceData<'src>>,
-    pub(crate) immutable_f32_whitelist: RefCell<BTreeSet<&'static str>>
+    pub(crate) immutable_f32_whitelist: BTreeSet<&'static str>
 }
 
 /// We need to collect interface data during the first pass, to be used later.
diff --git a/crates/webidl/src/lib.rs b/crates/webidl/src/lib.rs
index 2e11b128..637070c0 100644
--- a/crates/webidl/src/lib.rs
+++ b/crates/webidl/src/lib.rs
@@ -82,6 +82,8 @@ fn parse(webidl_source: &str, allowed_types: Option<&[&str]>) -> Result<Program>
 
     let mut first_pass_record: FirstPassRecord = Default::default();
     first_pass_record.builtin_idents = builtin_idents();
+    first_pass_record.immutable_f32_whitelist = immutable_f32_whitelist();
+
     definitions.first_pass(&mut first_pass_record, ())?;
     let mut program = Default::default();
     let mut submodules = Vec::new();
@@ -179,6 +181,26 @@ fn builtin_idents() -> BTreeSet<Ident> {
     )
 }
 
+fn immutable_f32_whitelist() -> BTreeSet<&'static str> {
+    BTreeSet::from_iter(
+        vec![
+            // WebGlRenderingContext
+            "uniform1fv",
+            "uniform2fv",
+            "uniform3fv",
+            "uniform4fv",
+            "uniformMatrix2fv",
+            "uniformMatrix3fv",
+            "uniformMatrix4fv",
+            "vertexAttrib1fv",
+            "vertexAttrib2fv",
+            "vertexAttrib3fv",
+            "vertexAttrib4fv",
+            // TODO: Add another type's functions here. Leave a comment header with the type name
+        ]
+    )
+}
+
 /// Run codegen on the AST to generate rust code.
 fn compile_ast(mut ast: Program) -> String {
     // Iteratively prune all entries from the AST which reference undefined
diff --git a/crates/webidl/src/util.rs b/crates/webidl/src/util.rs
index 6e32767c..f0e89624 100644
--- a/crates/webidl/src/util.rs
+++ b/crates/webidl/src/util.rs
@@ -13,9 +13,6 @@ use weedle::literal::{ConstValue, FloatLit, IntegerLit};
 use first_pass::{FirstPassRecord, OperationData, OperationId, Signature};
 use idl_type::{IdlType, ToIdlType};
 
-use std::collections::BTreeSet;
-use std::cell::Ref;
-
 /// For variadic operations an overload with a `js_sys::Array` argument is generated alongside with
 /// `operation_name_0`, `operation_name_1`, `operation_name_2`, ..., `operation_name_n` overloads
 /// which have the count of arguments for passing values to the variadic argument
@@ -651,7 +648,7 @@ impl<'src> FirstPassRecord<'src> {
             _ => return idl_type
         };
 
-        if self.immutable_f32_whitelist().contains(op) {
+        if self.immutable_f32_whitelist.contains(op) {
             flag_slices_immutable(&mut idl_type)
         }
 
@@ -660,29 +657,7 @@ impl<'src> FirstPassRecord<'src> {
         idl_type
     }
 
-    fn immutable_f32_whitelist(&self) -> Ref<BTreeSet<&'static str>> {
-        if self.immutable_f32_whitelist.borrow().len() == 0 {
-            *self.immutable_f32_whitelist.borrow_mut() = vec![
-                // WebGlRenderingContext
-                "uniform1fv",
-                "uniform2fv",
-                "uniform3fv",
-                "uniform4fv",
-                "uniformMatrix2fv",
-                "uniformMatrix3fv",
-                "uniformMatrix4fv",
-                "vertexAttrib1fv",
-                "vertexAttrib2fv",
-                "vertexAttrib3fv",
-                "vertexAttrib4fv",
-                // TODO: Add another type's functions here. Leave a comment header with the type name
-            ]
-                .into_iter()
-                .collect();
-        }
 
-        self.immutable_f32_whitelist.borrow()
-    }
 }
 
 /// Search for an attribute by name in some webidl object's attributes.