diff --git a/CHANGELOG.md b/CHANGELOG.md
index cabf1d8..f73df10 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,10 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
+## [1.12.11] - Unreleased
+### Fixed
+- Improved error if the source is not a string.
+
 ## [1.12.10] - 2024-07-17
 ### Fixed
 - `auto_trim` plugin throws if there are no next tokens [#73].
@@ -252,6 +256,7 @@ First version
 [#72]: https://github.com/oscarotero/vento/issues/72
 [#73]: https://github.com/oscarotero/vento/issues/73
 
+[1.12.11]: https://github.com/oscarotero/vento/compare/v1.12.10...HEAD
 [1.12.10]: https://github.com/oscarotero/vento/compare/v0.12.9...v1.12.10
 [0.12.9]: https://github.com/oscarotero/vento/compare/v0.12.8...v0.12.9
 [0.12.8]: https://github.com/oscarotero/vento/compare/v0.12.7...v0.12.8
diff --git a/src/environment.ts b/src/environment.ts
index 37190ff..c90d65a 100644
--- a/src/environment.ts
+++ b/src/environment.ts
@@ -125,6 +125,11 @@ export class Environment {
     defaults?: Record<string, unknown>,
     sync = false,
   ): Template | TemplateSync {
+    if (typeof source !== "string") {
+      throw new Error(
+        `The source code of "${path}" must be a string. Got ${typeof source}`,
+      );
+    }
     const tokens = this.tokenize(source, path);
     let code = this.compileTokens(tokens).join("\n");