diff --git a/src/ast/ast-types.ts b/src/ast/ast-types.ts
index 850dec1..8449d6f 100644
--- a/src/ast/ast-types.ts
+++ b/src/ast/ast-types.ts
@@ -4,7 +4,7 @@
  * *AstNode* types where I was lazy or didn't know the core type.
  */
 
-import { Scope } from '../parser/scope';
+import { Scope } from '../parser/scope.js';
 
 // The overall result of parsing, which incldues the AST and scopes
 export interface Program {
diff --git a/src/ast/ast.test.ts b/src/ast/ast.test.ts
index 593f694..c99e82e 100644
--- a/src/ast/ast.test.ts
+++ b/src/ast/ast.test.ts
@@ -1,5 +1,10 @@
-import { AstNode, BinaryNode, IdentifierNode, LiteralNode } from './ast-types';
-import { visit } from './visit';
+import {
+  AstNode,
+  BinaryNode,
+  IdentifierNode,
+  LiteralNode,
+} from './ast-types.js';
+import { visit } from './visit.js';
 
 const literal = <T>(literal: T): LiteralNode<T> => ({
   type: 'literal',
diff --git a/src/ast/ast.ts b/src/ast/ast.ts
index 868962b..18a6919 100644
--- a/src/ast/ast.ts
+++ b/src/ast/ast.ts
@@ -1,4 +1,4 @@
-import type { AstNode, Program } from './ast-types';
+import type { AstNode, Program } from './ast-types.js';
 
 type NodeGenerator<NodeType> = (node: NodeType) => string;
 
diff --git a/src/ast/index.ts b/src/ast/index.ts
index 94b3dd9..8810bf8 100644
--- a/src/ast/index.ts
+++ b/src/ast/index.ts
@@ -1,3 +1,3 @@
-export * from './ast';
-export * from './visit';
-export * from './ast-types';
+export * from './ast.js';
+export * from './visit.js';
+export * from './ast-types.js';
diff --git a/src/ast/visit.ts b/src/ast/visit.ts
index 5f91d10..522102c 100644
--- a/src/ast/visit.ts
+++ b/src/ast/visit.ts
@@ -1,4 +1,4 @@
-import type { AstNode, Program } from './ast-types';
+import type { AstNode, Program } from './ast-types.js';
 
 const isNode = (node: AstNode) => !!node?.type;
 const isTraversable = (node: any) => isNode(node) || Array.isArray(node);
diff --git a/src/index.ts b/src/index.ts
index f8d1902..9e35188 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,6 +1,6 @@
-import generate from './parser/generator';
-import parser from './parser/parser';
+import generate from './parser/generator.js';
+import * as parser from './parser/parser.js';
 
-export type * from './error';
+export type * from './error.js';
 
 export { generate, parser };
diff --git a/src/parser/generator.ts b/src/parser/generator.ts
index 8b0622c..14bfd72 100644
--- a/src/parser/generator.ts
+++ b/src/parser/generator.ts
@@ -1,4 +1,8 @@
-import { makeGenerator, makeEveryOtherGenerator, NodeGenerators } from '../ast';
+import {
+  makeGenerator,
+  makeEveryOtherGenerator,
+  NodeGenerators,
+} from '../ast/index.js';
 
 const generators: NodeGenerators = {
   program: (node) => generate(node.wsStart) + generate(node.program),
diff --git a/src/parser/grammar.ts b/src/parser/grammar.ts
index 64c3a5f..eb289c4 100644
--- a/src/parser/grammar.ts
+++ b/src/parser/grammar.ts
@@ -16,8 +16,8 @@ import {
   TypeNameNode,
   FullySpecifiedTypeNode,
   TypeSpecifierNode,
-} from '../ast';
-import { ParserOptions } from './parser';
+} from '../ast/index.js';
+import { ParserOptions } from './parser.js';
 import {
   Scope,
   findGlobalScope,
@@ -30,7 +30,7 @@ import {
   isDeclaredType,
   makeScopeIndex,
   findBindingScope,
-} from './scope';
+} from './scope.js';
 
 export {
   Scope,
diff --git a/src/parser/parse.test.ts b/src/parser/parse.test.ts
index 5108551..e088a31 100644
--- a/src/parser/parse.test.ts
+++ b/src/parser/parse.test.ts
@@ -1,6 +1,6 @@
-import { FunctionCallNode, visit } from '../ast';
-import { GlslSyntaxError } from '../error';
-import { buildParser } from './test-helpers';
+import { FunctionCallNode, visit } from '../ast/index.js';
+import { GlslSyntaxError } from '../error.js';
+import { buildParser } from './test-helpers.js';
 
 let c!: ReturnType<typeof buildParser>;
 beforeAll(() => (c = buildParser()));
diff --git a/src/parser/scope.test.ts b/src/parser/scope.test.ts
index 81cf626..d3e9733 100644
--- a/src/parser/scope.test.ts
+++ b/src/parser/scope.test.ts
@@ -1,7 +1,7 @@
-import generate from './generator';
-import { renameBindings, renameFunctions, renameTypes } from './utils';
-import { UNKNOWN_TYPE } from './grammar';
-import { buildParser, nextWarn } from './test-helpers';
+import generate from './generator.js';
+import { renameBindings, renameFunctions, renameTypes } from './utils.js';
+import { UNKNOWN_TYPE } from './grammar.js';
+import { buildParser, nextWarn } from './test-helpers.js';
 
 let c!: ReturnType<typeof buildParser>;
 beforeAll(() => (c = buildParser()));
diff --git a/src/parser/scope.ts b/src/parser/scope.ts
index 9955f83..15b0bd5 100644
--- a/src/parser/scope.ts
+++ b/src/parser/scope.ts
@@ -9,8 +9,8 @@ import {
   FunctionNode,
   FunctionCallNode,
   TypeNameNode,
-} from '../ast';
-import { xor } from './utils';
+} from '../ast/index.js';
+import { xor } from './utils.js';
 
 export type TypeScopeEntry = {
   declaration?: TypeNameNode;
diff --git a/src/parser/test-helpers.ts b/src/parser/test-helpers.ts
index deb937f..90cb8d3 100644
--- a/src/parser/test-helpers.ts
+++ b/src/parser/test-helpers.ts
@@ -1,10 +1,10 @@
 import { execSync } from 'child_process';
 import { GrammarError } from 'peggy';
 import util from 'util';
-import generate from './generator';
-import { AstNode, FunctionNode, Program } from '../ast';
-import { Parse, ParserOptions } from './parser';
-import { FunctionScopeIndex, Scope, ScopeIndex } from './scope';
+import generate from './generator.js';
+import { AstNode, FunctionNode, Program } from '../ast/index.js';
+import { Parse, ParserOptions } from './parser.js';
+import { FunctionScopeIndex, Scope, ScopeIndex } from './scope.js';
 
 export const inspect = (arg: any) =>
   console.log(util.inspect(arg, false, null, true));
diff --git a/src/parser/utils.ts b/src/parser/utils.ts
index 8ae9eed..78438b7 100644
--- a/src/parser/utils.ts
+++ b/src/parser/utils.ts
@@ -1,5 +1,5 @@
-import type { AstNode } from '../ast';
-import { Scope } from './scope';
+import type { AstNode } from '../ast/index.js';
+import { Scope } from './scope.js';
 
 export const renameBindings = (
   scope: Scope,
diff --git a/src/preprocessor/generator.ts b/src/preprocessor/generator.ts
index c615754..d557f07 100644
--- a/src/preprocessor/generator.ts
+++ b/src/preprocessor/generator.ts
@@ -1,6 +1,6 @@
-import { makeGenerator, NodeGenerators } from '../ast';
-import { PreprocessorProgram } from './preprocessor';
-import { PreprocessorAstNode } from './preprocessor-node';
+import { makeGenerator, NodeGenerators } from '../ast/index.js';
+import { PreprocessorProgram } from './preprocessor.js';
+import { PreprocessorAstNode } from './preprocessor-node.js';
 
 type NodeGenerator<NodeType> = (node: NodeType) => string;
 
diff --git a/src/preprocessor/index.ts b/src/preprocessor/index.ts
index d41a508..4c1a89c 100644
--- a/src/preprocessor/index.ts
+++ b/src/preprocessor/index.ts
@@ -1,13 +1,13 @@
-import generate from './generator';
+import generate from './generator.js';
 import {
   preprocessAst,
   preprocessComments,
   PreprocessorOptions,
-} from './preprocessor';
+} from './preprocessor.js';
 
 // This index file is currently only for package publishing, where the whole
 // library exists in the dist/ folder, so the below import is relative to dist/
-import parser from './preprocessor-parser.js';
+import * as parser from './preprocessor-parser.js';
 
 // Should this be in a separate file? There's no tests for it either
 const preprocess = (src: string, options: PreprocessorOptions) =>
diff --git a/src/preprocessor/preprocessor.test.ts b/src/preprocessor/preprocessor.test.ts
index 322afb0..d5ef685 100644
--- a/src/preprocessor/preprocessor.test.ts
+++ b/src/preprocessor/preprocessor.test.ts
@@ -5,9 +5,9 @@ import {
   preprocessComments,
   preprocessAst,
   PreprocessorProgram,
-} from './preprocessor';
-import generate from './generator';
-import { GlslSyntaxError } from '../error';
+} from './preprocessor.js';
+import generate from './generator.js';
+import { GlslSyntaxError } from '../error.js';
 
 const fileContents = (filePath: string): string =>
   fs.readFileSync(filePath).toString();
diff --git a/src/preprocessor/preprocessor.ts b/src/preprocessor/preprocessor.ts
index e666653..a07ed47 100644
--- a/src/preprocessor/preprocessor.ts
+++ b/src/preprocessor/preprocessor.ts
@@ -1,4 +1,4 @@
-import { NodeVisitor, Path, visit } from '../ast/visit';
+import { NodeVisitor, Path, visit } from '../ast/visit.js';
 import {
   PreprocessorAstNode,
   PreprocessorElseIfNode,
@@ -6,7 +6,7 @@ import {
   PreprocessorIfNode,
   PreprocessorLiteralNode,
   PreprocessorSegmentNode,
-} from './preprocessor-node';
+} from './preprocessor-node.js';
 
 export type PreprocessorProgram = {
   type: string;
diff --git a/tsconfig.json b/tsconfig.json
index b0250ed..1bb622b 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -9,14 +9,16 @@
     "lib": ["ESNext"],
 
     // Create ESM modules
-    "module": "esnext",
+    "module": "NodeNext",
     // Specify multiple folders that act like `./node_modules/@types`
     "typeRoots": [
       "node_modules/@types",
       "./preprocessor",
       "./parser"
-      ],          
-      
+    ],
+
+    "moduleResolution": "NodeNext",
+
     // Generate .d.ts files from TypeScript and JavaScript files in your project
     "declaration": true,
     // Specify an output folder for all emitted files.