diff --git a/example/demo_gen/demo/FixedDecimal.mjs b/example/demo_gen/demo/FixedDecimal.mjs
index 49faa7f24..428f1d642 100644
--- a/example/demo_gen/demo/FixedDecimal.mjs
+++ b/example/demo_gen/demo/FixedDecimal.mjs
@@ -1,13 +1,12 @@
 import { FixedDecimal } from "../../js/lib/api/index.mjs"
-export function toString() {
-    var terminusArgs = arguments;
+export function toString(v) {
     return (function (...args) { return args[0].toString(...args.slice(1)) }).apply(
         null,
         [
             FixedDecimal.new_.apply(
                 null,
                 [
-                    terminusArgs[0]
+                    v
                 ]
             )
         ]
diff --git a/example/demo_gen/demo/FixedDecimalFormatter.mjs b/example/demo_gen/demo/FixedDecimalFormatter.mjs
index 7e53e38f3..312cca8fd 100644
--- a/example/demo_gen/demo/FixedDecimalFormatter.mjs
+++ b/example/demo_gen/demo/FixedDecimalFormatter.mjs
@@ -3,8 +3,7 @@ import { FixedDecimal } from "../../js/lib/api/index.mjs"
 import { FixedDecimalFormatter } from "../../js/lib/api/index.mjs"
 import { FixedDecimalFormatterOptions } from "../../js/lib/api/index.mjs"
 import { Locale } from "../../js/lib/api/index.mjs"
-export function formatWrite() {
-    var terminusArgs = arguments;
+export function formatWrite(name, grouping_strategy, some_other_config, v) {
     return (function (...args) { return args[0].formatWrite(...args.slice(1)) }).apply(
         null,
         [
@@ -14,7 +13,7 @@ export function formatWrite() {
                     Locale.new_.apply(
                         null,
                         [
-                            terminusArgs[0]
+                            name
                         ]
                     ),
                     DataProvider.newStatic.apply(
@@ -27,8 +26,8 @@ export function formatWrite() {
                     }).apply(
                         null,
                         [
-                            terminusArgs[1],
-                            terminusArgs[2]
+                            grouping_strategy,
+                            some_other_config
                         ]
                     )
                 ]
@@ -36,7 +35,7 @@ export function formatWrite() {
             FixedDecimal.new_.apply(
                 null,
                 [
-                    terminusArgs[3]
+                    v
                 ]
             )
         ]
diff --git a/feature_tests/demo_gen/demo/Float64Vec.mjs b/feature_tests/demo_gen/demo/Float64Vec.mjs
index 7d78f0ff3..f321848ce 100644
--- a/feature_tests/demo_gen/demo/Float64Vec.mjs
+++ b/feature_tests/demo_gen/demo/Float64Vec.mjs
@@ -1,13 +1,12 @@
 import { Float64Vec } from "../../js/api/index.mjs"
-export function toString() {
-    var terminusArgs = arguments;
+export function toString(v) {
     return (function (...args) { return args[0].toString(...args.slice(1)) }).apply(
         null,
         [
             Float64Vec.newFromOwned.apply(
                 null,
                 [
-                    terminusArgs[0]
+                    v
                 ]
             )
         ]
diff --git a/feature_tests/demo_gen/demo/MyString.mjs b/feature_tests/demo_gen/demo/MyString.mjs
index 6e1934cf1..efba98356 100644
--- a/feature_tests/demo_gen/demo/MyString.mjs
+++ b/feature_tests/demo_gen/demo/MyString.mjs
@@ -1,24 +1,22 @@
 import { MyString } from "../../js/api/index.mjs"
-export function getStr() {
-    var terminusArgs = arguments;
+export function getStr(v) {
     return (function (...args) { return args[0].getStr }).apply(
         null,
         [
             MyString.new_.apply(
                 null,
                 [
-                    terminusArgs[0]
+                    v
                 ]
             )
         ]
     );
 }
-export function stringTransform() {
-    var terminusArgs = arguments;
+export function stringTransform(foo) {
     return MyString.stringTransform.apply(
         null,
         [
-            terminusArgs[0]
+            foo
         ]
     );
 }
diff --git a/feature_tests/demo_gen/demo/Opaque.mjs b/feature_tests/demo_gen/demo/Opaque.mjs
index 885269b7b..626b27275 100644
--- a/feature_tests/demo_gen/demo/Opaque.mjs
+++ b/feature_tests/demo_gen/demo/Opaque.mjs
@@ -1,6 +1,5 @@
 import { Opaque } from "../../js/api/index.mjs"
 export function getDebugStr() {
-    var terminusArgs = arguments;
     return (function (...args) { return args[0].getDebugStr(...args.slice(1)) }).apply(
         null,
         [
diff --git a/feature_tests/demo_gen/demo/OptionString.mjs b/feature_tests/demo_gen/demo/OptionString.mjs
index 56828791e..d4401ca8b 100644
--- a/feature_tests/demo_gen/demo/OptionString.mjs
+++ b/feature_tests/demo_gen/demo/OptionString.mjs
@@ -1,13 +1,12 @@
 import { OptionString } from "../../js/api/index.mjs"
-export function write() {
-    var terminusArgs = arguments;
+export function write(diplomatStr) {
     return (function (...args) { return args[0].write(...args.slice(1)) }).apply(
         null,
         [
             OptionString.new_.apply(
                 null,
                 [
-                    terminusArgs[0]
+                    diplomatStr
                 ]
             )
         ]
diff --git a/feature_tests/demo_gen/demo/Utf16Wrap.mjs b/feature_tests/demo_gen/demo/Utf16Wrap.mjs
index 5c58b51ca..0ba39fba7 100644
--- a/feature_tests/demo_gen/demo/Utf16Wrap.mjs
+++ b/feature_tests/demo_gen/demo/Utf16Wrap.mjs
@@ -1,13 +1,12 @@
 import { Utf16Wrap } from "../../js/api/index.mjs"
-export function getDebugStr() {
-    var terminusArgs = arguments;
+export function getDebugStr(input) {
     return (function (...args) { return args[0].getDebugStr(...args.slice(1)) }).apply(
         null,
         [
             Utf16Wrap.fromUtf16.apply(
                 null,
                 [
-                    terminusArgs[0]
+                    input
                 ]
             )
         ]
diff --git a/tool/src/demo_gen/mod.rs b/tool/src/demo_gen/mod.rs
index 9bb72e263..2f21dc40e 100644
--- a/tool/src/demo_gen/mod.rs
+++ b/tool/src/demo_gen/mod.rs
@@ -3,7 +3,10 @@
 //! Designed to work in conjunction with the JS backend.
 //!
 //! See docs/demo_gen.md for more.
-use std::{collections::BTreeSet, fmt::Write};
+use std::{
+    collections::{BTreeSet, HashMap},
+    fmt::Write,
+};
 
 use askama::{self, Template};
 use diplomat_core::hir::{BackendAttrSupport, TypeContext};
@@ -201,6 +204,8 @@ pub(crate) fn run<'tcx>(
                         imports: BTreeSet::new(),
                     },
 
+                    out_param_collision: HashMap::new(),
+
                     relative_import_path: import_path.clone(),
                     module_name: module_name.clone(),
                 };
diff --git a/tool/src/demo_gen/terminus.rs b/tool/src/demo_gen/terminus.rs
index 5227f3eb5..c2cf9ed2e 100644
--- a/tool/src/demo_gen/terminus.rs
+++ b/tool/src/demo_gen/terminus.rs
@@ -1,4 +1,4 @@
-use std::collections::BTreeSet;
+use std::collections::{BTreeSet, HashMap};
 
 use diplomat_core::hir::{
     self, DemoInfo, Method, OpaqueDef, StructDef, StructPath, TyPosition, Type, TypeContext,
@@ -54,6 +54,9 @@ pub(super) struct RenderTerminusContext<'ctx, 'tcx> {
     pub errors: &'ctx ErrorStore<'tcx, String>,
     pub terminus_info: TerminusInfo,
 
+    /// To avoid similar parameter names while we're collecting [`OutParam`]s.
+    pub out_param_collision: HashMap<String, i32>,
+
     pub relative_import_path: String,
     pub module_name: String,
 }
@@ -236,8 +239,18 @@ impl<'ctx, 'tcx> RenderTerminusContext<'ctx, 'tcx> {
             }
         };
 
+        let (p, n) = if self.out_param_collision.contains_key(&param_name) {
+            let n = self.out_param_collision.get(&param_name).unwrap();
+
+            (format!("{param_name}_{n}"), n + 1)
+        } else {
+            (param_name.clone(), 1)
+        };
+
+        self.out_param_collision.insert(param_name, n);
+
         let out_param = OutParam {
-            param_name,
+            param_name: p.clone(),
             label,
             type_name: type_name.clone(),
             type_use,
@@ -246,10 +259,7 @@ impl<'ctx, 'tcx> RenderTerminusContext<'ctx, 'tcx> {
 
         self.terminus_info.out_params.push(out_param);
 
-        let param_info = ParamInfo {
-            // Grab arguments without having to name them
-            js: format!("terminusArgs[{}]", self.terminus_info.out_params.len() - 1),
-        };
+        let param_info = ParamInfo { js: p };
 
         node.params.push(param_info);
     }
diff --git a/tool/templates/demo_gen/terminus.js.jinja b/tool/templates/demo_gen/terminus.js.jinja
index 174a1b5e5..1a8f638b3 100644
--- a/tool/templates/demo_gen/terminus.js.jinja
+++ b/tool/templates/demo_gen/terminus.js.jinja
@@ -1,9 +1,8 @@
 export function {{function_name}}(
-    {%- if typescript %}{%- for param in out_params -%}
+    {%- for param in out_params -%}
     {{param.param_name}}{% if typescript %}: {{param.type_name}}{% endif %}{% if !loop.last %}, {% endif %}
-    {%- endfor -%}{% endif -%}
+    {%- endfor -%}
 ){% if typescript %};{% else %} {
-    var terminusArgs = arguments;
     return {{node_call_stack|indent(4)}};
 }
 {%- endif %}
\ No newline at end of file