diff --git a/ext/gd/libgd/gd.c b/ext/gd/libgd/gd.c
index 71a0e9ea63f22..7602203613d83 100644
--- a/ext/gd/libgd/gd.c
+++ b/ext/gd/libgd/gd.c
@@ -2326,8 +2326,47 @@ void gdImageFilledRectangle (gdImagePtr im, int x1, int y1, int x2, int y2, int
 	_gdImageFilledVRectangle(im, x1, y1, x2, y2, color);
 }
 
+static int _gdValidateCopyRectBounds(
+	const gdImagePtr dst,
+	const gdImagePtr src,
+	int dstX, int dstY,
+	int srcX, int srcY,
+	int w, int h
+) {
+	/* Check for null pointers */
+	if (!dst || !src) {
+		return 0;
+	}
+
+	/* Check for overflow in dstX + w */
+	if (w > 0 && dstX > INT_MAX - w) {
+		return 0;
+	}
+
+	/* Check for overflow in dstY + h */
+	if (h > 0 && dstY > INT_MAX - h) {
+		return 0;
+	}
+
+	/* Check for overflow in srcX + w */
+	if (w > 0 && srcX > INT_MAX - w) {
+		return 0;
+	}
+
+	/* Check for overflow in srcY + h */
+	if (h > 0 && srcY > INT_MAX - h) {
+		return 0;
+	}
+
+	return 1;
+}
+
 void gdImageCopy (gdImagePtr dst, gdImagePtr src, int dstX, int dstY, int srcX, int srcY, int w, int h)
 {
+	if (!_gdValidateCopyRectBounds(dst, src, dstX, dstY, srcX, srcY, w, h)) {
+		return;
+	}
+
 	int c;
 	int x, y;
 	int tox, toy;
@@ -2409,6 +2448,10 @@ void gdImageCopy (gdImagePtr dst, gdImagePtr src, int dstX, int dstY, int srcX,
    so it doesn't pay attention to the alpha channel. */
 void gdImageCopyMerge (gdImagePtr dst, gdImagePtr src, int dstX, int dstY, int srcX, int srcY, int w, int h, int pct)
 {
+	if (!_gdValidateCopyRectBounds(dst, src, dstX, dstY, srcX, srcY, w, h)) {
+		return;
+	}
+
 	int c, dc;
 	int x, y;
 	int tox, toy;
@@ -2449,6 +2492,10 @@ void gdImageCopyMerge (gdImagePtr dst, gdImagePtr src, int dstX, int dstY, int s
    so it doesn't pay attention to the alpha channel. */
 void gdImageCopyMergeGray (gdImagePtr dst, gdImagePtr src, int dstX, int dstY, int srcX, int srcY, int w, int h, int pct)
 {
+	if (!_gdValidateCopyRectBounds(dst, src, dstX, dstY, srcX, srcY, w, h)) {
+		return;
+	}
+
 	int c, dc;
 	int x, y;
 	int tox, toy;
@@ -2503,6 +2550,14 @@ void gdImageCopyMergeGray (gdImagePtr dst, gdImagePtr src, int dstX, int dstY, i
 
 void gdImageCopyResized (gdImagePtr dst, gdImagePtr src, int dstX, int dstY, int srcX, int srcY, int dstW, int dstH, int srcW, int srcH)
 {
+	if (!_gdValidateCopyRectBounds(dst, src, dstX, dstY, srcX, srcY, dstW, dstH)) {
+		return;
+	}
+
+	if (!_gdValidateCopyRectBounds(dst, src, dstX, dstY, srcX, srcY, srcW, srcH)) {
+		return;
+	}
+
 	int c;
 	int x, y;
 	int tox, toy;
@@ -2613,6 +2668,14 @@ void gdImageCopyResized (gdImagePtr dst, gdImagePtr src, int dstX, int dstY, int
 
 void gdImageCopyResampled (gdImagePtr dst, gdImagePtr src, int dstX, int dstY, int srcX, int srcY, int dstW, int dstH, int srcW, int srcH)
 {
+	if (!_gdValidateCopyRectBounds(dst, src, dstX, dstY, srcX, srcY, dstW, dstH)) {
+		return;
+	}
+
+	if (!_gdValidateCopyRectBounds(dst, src, dstX, dstY, srcX, srcY, srcW, srcH)) {
+		return;
+	}
+
 	int x, y;
 	double sy1, sy2, sx1, sx2;
 
diff --git a/ext/gd/tests/gh21163.phpt b/ext/gd/tests/gh21163.phpt
new file mode 100644
index 0000000000000..46f9c76266f8b
--- /dev/null
+++ b/ext/gd/tests/gh21163.phpt
@@ -0,0 +1,79 @@
+--TEST--
+GH-17772 (prevents signed int overflow in gdImageCopy functions)
+--EXTENSIONS--
+gd
+--SKIPIF--
+<?php
+if (!GD_BUNDLED) die("skip requires bundled GD library");
+?>
+--FILE--
+<?php
+function makeImages(): array {
+    $dst = imagecreatetruecolor(2, 2);
+    $src = imagecreatetruecolor(2, 2);
+
+    $blackDst = imagecolorallocate($dst, 0, 0, 0);
+    $whiteSrc = imagecolorallocate($src, 255, 255, 255);
+
+    imagefilledrectangle($dst, 0, 0, 1, 1, $blackDst);
+    imagefilledrectangle($src, 0, 0, 1, 1, $whiteSrc);
+
+    return [$dst, $src];
+}
+
+function assertDstUnchanged(string $label, $dst, int $expectedColor): void {
+    $actual = imagecolorat($dst, 0, 0);
+    if ($actual !== $expectedColor) {
+        echo "FAIL $label: dst changed, got $actual expected $expectedColor\n";
+        return;
+    }
+    echo "OK $label\n";
+}
+
+/*
+  Use values that will overflow a 32 bit signed int when adding w or h.
+  INT_MAX is 0x7fffffff.
+*/
+$nearIntMax = 0x7fffffff - 5;
+$w = 10;
+$h = 10;
+
+/* imagecopy */
+[$dst, $src] = makeImages();
+$expected = imagecolorat($dst, 0, 0);
+imagecopy($dst, $src, $nearIntMax, 0, 0, 0, $w, $h);
+assertDstUnchanged('imagecopy', $dst, $expected);
+
+/* imagecopymerge */
+[$dst, $src] = makeImages();
+$expected = imagecolorat($dst, 0, 0);
+imagecopymerge($dst, $src, $nearIntMax, 0, 0, 0, $w, $h, 50);
+assertDstUnchanged('imagecopymerge', $dst, $expected);
+
+/* imagecopymergegray */
+[$dst, $src] = makeImages();
+$expected = imagecolorat($dst, 0, 0);
+imagecopymergegray($dst, $src, $nearIntMax, 0, 0, 0, $w, $h, 50);
+assertDstUnchanged('imagecopymergegray', $dst, $expected);
+
+/* imagecopyresized */
+[$dst, $src] = makeImages();
+$expected = imagecolorat($dst, 0, 0);
+imagecopyresized($dst, $src, $nearIntMax, 0, 0, 0, $w, $h, 1, 1);
+assertDstUnchanged('imagecopyresized', $dst, $expected);
+
+/* imagecopyresampled */
+[$dst, $src] = makeImages();
+$expected = imagecolorat($dst, 0, 0);
+imagecopyresampled($dst, $src, $nearIntMax, 0, 0, 0, $w, $h, 1, 1);
+assertDstUnchanged('imagecopyresampled', $dst, $expected);
+
+echo "done\n";
+?>
+--EXPECT--
+OK imagecopy
+OK imagecopymerge
+OK imagecopymergegray
+OK imagecopyresized
+OK imagecopyresampled
+done