diff --git a/ext/standard/pack.c b/ext/standard/pack.c
index 6abdc98bd6d..8f72164a269 100644
--- a/ext/standard/pack.c
+++ b/ext/standard/pack.c
@@ -979,6 +979,13 @@ PHP_FUNCTION(unpack)
 						zend_string *buf;
 						zend_long ipos, opos;
 
+
+						if (size > INT_MAX / 2) {
+							zend_string_release(real_name);
+							zend_argument_value_error(1, "repeater must be less than or equal to %d", INT_MAX / 2);
+							RETURN_THROWS();
+						}
+
 						/* If size was given take minimum of len and size */
 						if (size >= 0 && len > (size * 2)) {
 							len = size * 2;
diff --git a/ext/standard/tests/strings/gh15613.phpt b/ext/standard/tests/strings/gh15613.phpt
new file mode 100644
index 00000000000..8f40ee820c9
--- /dev/null
+++ b/ext/standard/tests/strings/gh15613.phpt
@@ -0,0 +1,25 @@
+--TEST--
+GH-15613 overflow on hex strings repeater value
+--SKIPIF--
+<?php
+if (PHP_INT_SIZE != 8) die("skip this test is for 64 bit platform only");
+?>
+--INI--
+memory_limit=-1
+--FILE--
+<?php
+try {
+	unpack('h2147483647', str_repeat('X', 2**31 + 10));
+} catch (\ValueError $e) {
+	echo $e->getMessage() . PHP_EOL;
+}
+
+try {
+	unpack('H2147483647', str_repeat('X', 2**31 + 10));
+} catch (\ValueError $e) {
+	echo $e->getMessage();
+}
+?>
+--EXPECTF--
+unpack(): Argument #1 ($format) repeater must be less than or equal to %d
+unpack(): Argument #1 ($format) repeater must be less than or equal to %d