diff --git a/Zend/tests/gh13670_001.phpt b/Zend/tests/gh13670_001.phpt
new file mode 100644
index 0000000000000..def8fa3f5f25e
--- /dev/null
+++ b/Zend/tests/gh13670_001.phpt
@@ -0,0 +1,43 @@
+--TEST--
+GH-13670 001
+--FILE--
+<?php
+
+register_shutdown_function(function () {
+    global $shutdown;
+    $shutdown = true;
+});
+
+class Cycle {
+    public $self;
+    public function __construct() {
+        $this->self = $this;
+    }
+    public function __destruct() {
+        global $shutdown;
+        if (!$shutdown) {
+            new Cycle();
+        }
+    }
+}
+
+$defaultThreshold = gc_status()['threshold'];
+for ($i = 0; $i < $defaultThreshold+1; $i++) {
+    new Cycle();
+}
+
+$objs = [];
+for ($i = 0; $i < 100; $i++) {
+    $obj = new stdClass;
+    $objs[] = $obj;
+}
+
+$st = gc_status();
+
+if ($st['runs'] > 10) {
+    var_dump($st);
+}
+?>
+==DONE==
+--EXPECT--
+==DONE==
diff --git a/Zend/tests/gh13670_002.phpt b/Zend/tests/gh13670_002.phpt
new file mode 100644
index 0000000000000..c822585e3632f
--- /dev/null
+++ b/Zend/tests/gh13670_002.phpt
@@ -0,0 +1,66 @@
+--TEST--
+GH-13670 002
+--FILE--
+<?php
+
+register_shutdown_function(function () {
+    global $shutdown;
+    $shutdown = true;
+});
+
+class Cycle {
+    public $self;
+    public function __construct() {
+        $this->self = $this;
+    }
+}
+
+class Canary {
+    public $self;
+    public function __construct() {
+        $this->self = $this;
+    }
+    public function __destruct() {
+        global $shutdown;
+        if (!$shutdown) {
+            work();
+        }
+    }
+}
+
+function work() {
+    global $objs, $defaultThreshold;
+    new Canary();
+    // Create some collectable garbage so the next run will not adjust
+    // threshold
+    for ($i = 0; $i < 100; $i++) {
+        new Cycle();
+    }
+    // Add potential garbage to buffer
+    foreach (array_slice($objs, 0, $defaultThreshold) as $obj) {
+        $o = $obj;
+    }
+}
+
+$defaultThreshold = gc_status()['threshold'];
+$objs = [];
+for ($i = 0; $i < $defaultThreshold*2; $i++) {
+    $obj = new stdClass;
+    $objs[] = $obj;
+}
+
+work();
+
+foreach ($objs as $obj) {
+    $o = $obj;
+}
+
+$st = gc_status();
+
+if ($st['runs'] > 10) {
+    var_dump($st);
+}
+?>
+==DONE==
+--EXPECT--
+==DONE==
diff --git a/Zend/tests/gh13670_003.phpt b/Zend/tests/gh13670_003.phpt
new file mode 100644
index 0000000000000..defd3da438678
--- /dev/null
+++ b/Zend/tests/gh13670_003.phpt
@@ -0,0 +1,68 @@
+--TEST--
+GH-13670 003
+--FILE--
+<?php
+
+register_shutdown_function(function () {
+    global $shutdown;
+    $shutdown = true;
+});
+
+class Cycle {
+    public $self;
+    public function __construct() {
+        $this->self = $this;
+    }
+}
+
+class Canary {
+    public $self;
+    public function __construct() {
+        $this->self = $this;
+    }
+    public function __destruct() {
+        global $shutdown;
+        if (!$shutdown) {
+            work();
+        }
+    }
+}
+
+function work() {
+    global $objs, $defaultThreshold;
+    new Canary();
+    // Create some collectable garbage so the next run will not adjust
+    // threshold
+    for ($i = 0; $i < 100; $i++) {
+        new Cycle();
+    }
+    // Add potential garbage to buffer
+    foreach (array_slice($objs, 0, $defaultThreshold) as $obj) {
+        $o = $obj;
+    }
+}
+
+$defaultThreshold = gc_status()['threshold'];
+$objs = [];
+for ($i = 0; $i < $defaultThreshold*2; $i++) {
+    $obj = new stdClass;
+    $objs[] = $obj;
+}
+
+work();
+
+// Result of array_slice() is a tmpvar that will be checked by
+// zend_gc_check_root_tmpvars()
+foreach (array_slice($objs, -10) as $obj) {
+    $o = $obj;
+}
+
+$st = gc_status();
+
+if ($st['runs'] > 10) {
+    var_dump($st);
+}
+?>
+==DONE==
+--EXPECT--
+==DONE==
diff --git a/Zend/zend_gc.c b/Zend/zend_gc.c
index e7d9c8ef29257..4417f674cbb91 100644
--- a/Zend/zend_gc.c
+++ b/Zend/zend_gc.c
@@ -557,7 +557,7 @@ static void gc_adjust_threshold(int count)
 	/* TODO Very simple heuristic for dynamic GC buffer resizing:
 	 * If there are "too few" collections, increase the collection threshold
 	 * by a fixed step */
-	if (count < GC_THRESHOLD_TRIGGER) {
+	if (count < GC_THRESHOLD_TRIGGER || GC_G(num_roots) >= GC_G(gc_threshold)) {
 		/* increase */
 		if (GC_G(gc_threshold) < GC_THRESHOLD_MAX) {
 			new_threshold = GC_G(gc_threshold) + GC_THRESHOLD_STEP;
@@ -1674,7 +1674,13 @@ ZEND_API int zend_gc_collect_cycles(void)
 
 finish:
 	zend_get_gc_buffer_release();
+
+	/* Prevent GC from running during zend_gc_check_root_tmpvars, before
+	 * gc_threshold is adjusted, as this may result in unbounded recursion */
+	GC_G(gc_active) = 1;
 	zend_gc_check_root_tmpvars();
+	GC_G(gc_active) = 0;
+
 	return total_count;
 }