diff --git a/lib/classes/date.php b/lib/classes/date.php
index 6c97e05f45a..5338f023492 100644
--- a/lib/classes/date.php
+++ b/lib/classes/date.php
@@ -717,10 +717,10 @@ class core_date {
         // Windows format.
         $locale = $locale ?: get_string('locale', 'langconfig');
 
-        // The following code is taken from https://github.com/alphp/strftime without modifications.
+        // The following code is taken from https://github.com/alphp/strftime.
         // phpcs:disable
         if (!($timestamp instanceof DateTimeInterface)) {
-          $timestamp = is_int($timestamp) ? '@' . $timestamp : (string) $timestamp;
+          $timestamp = is_numeric($timestamp) ? '@' . $timestamp : (string) $timestamp;
 
           try {
             $timestamp = new DateTime($timestamp);
diff --git a/lib/tests/date_test.php b/lib/tests/date_test.php
index 74060fbe07e..c7dc89caef4 100644
--- a/lib/tests/date_test.php
+++ b/lib/tests/date_test.php
@@ -614,4 +614,65 @@ class date_test extends advanced_testcase {
             $this->assertSame($zone, $tz->getName());
         }
     }
+
+    /**
+     * Data provider for the values for test_core_strftime().
+     *
+     * @return array
+     */
+    public static function get_strftime_provider(): array {
+        return [
+            'string_c' => [
+                "1708405742",
+                null,
+                "20 February 2024 at 6:09 pm",
+            ],
+            'numeric_c' => [
+                1708405742,
+                null,
+                "20 February 2024 at 6:09 pm",
+            ],
+            'string_strftimedatetime' => [
+                "1708405742",
+                "strftimedatetime",
+                "20 February 2024, 06:09 PM",
+            ],
+            'numeric_strftimedatetime' => [
+                1708405742,
+                "strftimedatetime",
+                "20 February 2024, 06:09 PM",
+            ],
+            'string_strftimedatetimeshortaccurate' => [
+                "1708405742",
+                "strftimedatetimeshortaccurate",
+                "20/02/24, 18:09:02",
+            ],
+            'numeric_strftimedatetimeshortaccurate' => [
+                1708405742,
+                "strftimedatetimeshortaccurate",
+                "20/02/24, 18:09:02",
+            ],
+        ];
+    }
+
+    /**
+     * Test \core_date::strftime function.
+     *
+     * @dataProvider  get_strftime_provider
+     * @param mixed $input Input passed to strftime
+     * @param string|null $format The date format to pass to strftime, falls back to '%c' if null
+     * @param string $expected The output generated by strftime
+     *
+     * @covers \core_date::strftime
+     */
+    public function test_core_strftime(mixed $input, string|null $format, string $expected): void {
+        $this->resetAfterTest();
+        $this->setTimezone('Pacific/Auckland', 'Pacific/Auckland');
+        if (!$format) {
+            $format = "%c";
+        } else {
+            $format = get_string($format, 'langconfig');
+        }
+        $this->assertSame($expected, core_date::strftime($format, $input));
+    }
 }