diff --git a/ext/standard/pack.c b/ext/standard/pack.c
index 7b974cad16d..c9c118751bc 100644
--- a/ext/standard/pack.c
+++ b/ext/standard/pack.c
@@ -788,6 +788,10 @@ PHP_FUNCTION(unpack)
 			/* Never use any input */
 			case 'X':
 				size = -1;
+				if (arg < 0) {
+					php_error_docref(NULL, E_WARNING, "Type %c: '*' ignored", type);
+					arg = 1;
+				}
 				break;
 
 			case '@':
diff --git a/ext/standard/tests/strings/bug75075.phpt b/ext/standard/tests/strings/bug75075.phpt
new file mode 100644
index 00000000000..232de50622a
--- /dev/null
+++ b/ext/standard/tests/strings/bug75075.phpt
@@ -0,0 +1,10 @@
+--TEST--
+Bug #75075 (unpack with X* causes infinity loop)
+--FILE--
+<?php
+var_dump(unpack("X*", ""));
+?>
+--EXPECTF--
+Warning: unpack(): Type X: '*' ignored in %sbug75075.php on line %d
+array(0) {
+}