diff --git a/ext/gd/gd.c b/ext/gd/gd.c
index 5bcf11846316..c5daf5f430f5 100644
--- a/ext/gd/gd.c
+++ b/ext/gd/gd.c
@@ -4014,10 +4014,14 @@ PHP_FUNCTION(imagecropauto)
 			break;
 
 		case GD_CROP_THRESHOLD:
-			if (color < 0 || (!gdImageTrueColor(im) && color >= gdImageColorsTotal(im))) {
+			if (color < 0) {
 				zend_argument_value_error(4, "must be greater than or equal to 0 when using the threshold mode");
 				RETURN_THROWS();
 			}
+			if (!gdImageTrueColor(im) && color >= gdImageColorsTotal(im)) {
+				zend_argument_value_error(4, "must be a valid color index of the image when using the threshold mode");
+				RETURN_THROWS();
+			}
 			im_crop = gdImageCropThreshold(im, color, (float) threshold);
 			break;
 
diff --git a/ext/gd/tests/bug72494.phpt b/ext/gd/tests/bug72494.phpt
index 35e0359eae27..9e1b4cff65d3 100644
--- a/ext/gd/tests/bug72494.phpt
+++ b/ext/gd/tests/bug72494.phpt
@@ -14,4 +14,4 @@ trycatch_dump(
 
 ?>
 --EXPECT--
-!! [ValueError] imagecropauto(): Argument #4 ($color) must be greater than or equal to 0 when using the threshold mode
+!! [ValueError] imagecropauto(): Argument #4 ($color) must be a valid color index of the image when using the threshold mode
diff --git a/ext/gd/tests/imagecropauto_threshold_palette_color.phpt b/ext/gd/tests/imagecropauto_threshold_palette_color.phpt
new file mode 100644
index 000000000000..dc06fe08be7b
--- /dev/null
+++ b/ext/gd/tests/imagecropauto_threshold_palette_color.phpt
@@ -0,0 +1,21 @@
+--TEST--
+imagecropauto(): threshold mode, a color outside the palette
+--EXTENSIONS--
+gd
+--FILE--
+<?php
+$p = imagecreate(6, 6);
+imagecolorallocate($p, 255, 255, 255);
+imagecolorallocate($p, 10, 10, 10);
+foreach ([imagecolorstotal($p), -1, 1] as $color) {
+    try {
+        var_dump(imagecropauto($p, IMG_CROP_THRESHOLD, 0.5, $color) !== false);
+    } catch (Throwable $e) {
+        echo $e::class, ': ', $e->getMessage(), "\n";
+    }
+}
+?>
+--EXPECT--
+ValueError: imagecropauto(): Argument #4 ($color) must be a valid color index of the image when using the threshold mode
+ValueError: imagecropauto(): Argument #4 ($color) must be greater than or equal to 0 when using the threshold mode
+bool(true)