diff --git a/ext/gd/tests/bug47946.phpt b/ext/gd/tests/bug47946.phpt
new file mode 100644
index 00000000000..c84508509ce
--- /dev/null
+++ b/ext/gd/tests/bug47946.phpt
@@ -0,0 +1,51 @@
+--TEST--
+Bug #47946 (ImageConvolution overwrites background)
+--DESCRIPTION--
+The expected image has black pixel artifacts, what is another issue, though
+(perhaps #40158).
+--SKIPIF--
+<?php
+if (!extension_loaded('gd')) die('skip gd extension not available');
+?>
+--FILE--
+<?php
+function array_flatten($array)
+{
+    $tempArray = array();
+
+    foreach ($array as $value) {
+        if (is_array($value)) {
+            $tempArray = array_merge($tempArray, array_flatten($value));
+        } else {
+            $tempArray[] = $value;
+        }
+    }
+
+    return $tempArray;
+}
+
+function makeFilter($resource, $matrix, $offset = 1.0)
+{
+    $divisor = array_sum(array_flatten($matrix));
+    if ($divisor == 0) {
+        $divisor = .01;
+    }
+    return imageconvolution($resource, $matrix, $divisor, $offset);
+}
+
+$edgeMatrix = array(array(1, 0, 1), array(0, 5, 0), array(1, 0, 1));
+
+$im = imagecreatetruecolor(40, 40);
+imagealphablending($im, false);
+imagefilledrectangle($im, 0, 0, 39, 39, 0x7fffffff);
+imagefilledellipse($im, 19, 19, 20, 20, 0x00ff00);
+imagesavealpha($im, true);
+makeFilter($im, $edgeMatrix);
+
+require_once __DIR__ . '/func.inc';
+test_image_equals_file(__DIR__ . '/bug47946_exp.png', $im);
+?>
+===DONE===
+--EXPECT--
+The images are equal.
+===DONE===
diff --git a/ext/gd/tests/bug47946_exp.png b/ext/gd/tests/bug47946_exp.png
new file mode 100644
index 00000000000..7eb462dd883
Binary files /dev/null and b/ext/gd/tests/bug47946_exp.png differ