diff --git a/ext/hook.c b/ext/hook.c
index 1f2af89..09dd578 100644
--- a/ext/hook.c
+++ b/ext/hook.c
@@ -122,10 +122,12 @@ static inline void apply_interval(timelib_time **time, timelib_rel_time *interva
 		fci->params = _params; \
 		fci->named_params = NULL; \
 		fcc->function_handler = zend_hash_str_find_ptr(CG(function_table), #_name, strlen(#_name)); \
+		zif_handler hook_handler = fcc->function_handler->internal_function.handler; \
 		fcc->function_handler->internal_function.handler = COLOPL_TS_G(orig_##_name); \
 		fcc->called_scope = NULL; \
 		fcc->object = NULL; \
 		zend_call_function(fci, fcc); \
+		fcc->function_handler->internal_function.handler = hook_handler; \
 		efree(fci); \
 		efree(fcc); \
 	} while (0);
@@ -699,25 +701,11 @@ static void hook_strtotime(INTERNAL_FUNCTION_PARAMETERS)
 		return;
 	}
 
-	if (is_fixed_ret == 2) {
-		CALL_ORIGINAL_FUNCTION(strtotime);
-	} else {
-		/* Call original function with params. */
-		zval *params = NULL;
-		uint32_t param_count = 0;
-		zend_parse_parameters(ZEND_NUM_ARGS(), "+", &params, &param_count);
-		ZVAL_LONG(&params[1], get_shifted_time(NULL));
-		CALL_ORIGINAL_FUNCTION_WITH_PARAMS(strtotime, params, param_count);
-	}
-
-	/* Apply interval. */
-	timelib_time *t = timelib_time_ctor();
-	timelib_rel_time interval;
-	timelib_unixtime2gmt(t, Z_LVAL_P(return_value));
-	get_shift_interval(&interval);
-	apply_interval(&t, &interval);
-	RETVAL_LONG(timelib_date_to_int(t, NULL));
-	timelib_time_dtor(t);
+	/* Call original function based on shifted time */
+	zval params[2];
+	ZVAL_STR(&params[0], times);
+	ZVAL_LONG(&params[1], get_shifted_time(NULL));
+	CALL_ORIGINAL_FUNCTION_WITH_PARAMS(strtotime, params, 2);
 }
 
 #if HAVE_GETTIMEOFDAY
diff --git a/ext/tests/functions/strtotime_extra.phpt b/ext/tests/functions/strtotime_extra.phpt
deleted file mode 100644
index ea96580..0000000
--- a/ext/tests/functions/strtotime_extra.phpt
+++ /dev/null
@@ -1,30 +0,0 @@
---TEST--
-Check strtotime() extra pattern
---EXTENSIONS--
-colopl_timeshifter
---FILE--
-<?php declare(strict_types=1);
-
-$before = new \DateTime('@' . \strtotime('now'));
-
-\Colopl\ColoplTimeShifter\register_hook(new \DateInterval('P2Y'));
-
-$after_one = new \DateTime('@' . \strtotime('now'));
-$after_two = new \DateTime('@' . \strtotime('now'));
-
-$interval = $after_one->diff($before);
-
-if ($before == $after_one || $before == $after_two) {
-    die('failed');
-}
-
-/* Note: Sometime valgrind makes flaky: $interval->y !== 2 */
-if (($interval->y > 2 && $interval->y !== 0) || $interval->invert !== 0) {
-    die('failed');
-}
-
-die('success');
-
-?>
---EXPECT--
-success
diff --git a/ext/tests/gh13.phpt b/ext/tests/gh13.phpt
new file mode 100644
index 0000000..4bd6930
--- /dev/null
+++ b/ext/tests/gh13.phpt
@@ -0,0 +1,33 @@
+--TEST--
+Check GitHub Issue - #13 (strtotime extra pattern)
+--EXTENSIONS--
+colopl_timeshifter
+--FILE--
+<?php
+
+$before = new \DateTime('@' . \strtotime('now'));
+
+\Colopl\ColoplTimeShifter\register_hook(new \DateInterval('P2Y'));
+
+$after_one = new \DateTime('@' . \strtotime('now'));
+$after_two = new \DateTime('@' . \strtotime('now'));
+
+$interval = $after_one->diff($before);
+
+if ($before->getTimestamp() == $after_one->getTimestamp()) {
+    die('failed, $before == $after_one, ' . $before->format('Y-m-d H:i:s.u') . ' / ' . $after_one->format('Y-m-d H:i:s.u') . ' / ' . $after_two->format('Y-m-d H:i:s.u'));
+}
+if ($before->getTimestamp() == $after_two->getTimestamp()) {
+    die('failed, $before == $after_two, ' . $before->format('Y-m-d H:i:s.u') . ' / ' . $after_one->format('Y-m-d H:i:s.u') . ' / ' . $after_two->format('Y-m-d H:i:s.u'));
+}
+
+/* Note: Sometime valgrind makes flaky: $interval->y !== 2 */
+if (($interval->y > 2 && $interval->y !== 0) || $interval->invert !== 0) {
+    die('failed, $interval->y = ' . $interval->y . ', $interval->invert = ' . $interval->invert);
+}
+
+die('success');
+
+?>
+--EXPECT--
+success