diff --git a/types/assertions.d.ts b/types/assertions.d.ts
index 657ed3d486..8df254f67d 100644
--- a/types/assertions.d.ts
+++ b/types/assertions.d.ts
@@ -137,6 +137,12 @@ export interface DeepEqualAssertion {
 	 * `expected`, returning a boolean indicating whether the assertion passed.
 	 */
 	<Actual, Expected extends Actual>(actual: Actual, expected: Expected, message?: string): actual is Expected;
+	
+	/**
+	 * Assert that `actual` is [deeply equal](https://github.com/concordancejs/concordance#comparison-details) to
+	 * `expected`, returning a boolean indicating whether the assertion passed.
+	 */
+	<Actual extends Expected, Expected>(actual: Actual, expected: Expected, message?: string): expected is Actual;
 
 	/** Skip this assertion. */
 	skip(actual: any, expected: any, message?: string): void;