diff --git a/src/assert.ts b/src/assert.ts
index a05c062..d020399 100644
--- a/src/assert.ts
+++ b/src/assert.ts
@@ -5,9 +5,13 @@ export type { Equals } from "./Equals";
 
 /** @see <https://docs.tsafe.dev/assert#error-thrown> */
 export class AssertionError extends Error {
+    originalMessage?: string;
+
     constructor(msg: string | undefined) {
         super(`Wrong assertion encountered` + (!msg ? "" : `: "${msg}"`));
 
+        this.originalMessage = msg;
+
         Object.setPrototypeOf(this, new.target.prototype);
 
         if (!this.stack) {
diff --git a/test/assertIs.ts b/test/assertIs.ts
index 3c8855c..6f6decf 100644
--- a/test/assertIs.ts
+++ b/test/assertIs.ts
@@ -122,3 +122,12 @@ scope: {
         console.log("PASS");
     }
 }
+
+/**
+ * `AssertionError` should store the original message in the `originalMessage` property.
+ */
+{
+    const error = new AssertionError("message");
+    assert(error.originalMessage === "message");
+    console.log("PASS");
+}