diff --git a/NEWS b/NEWS
index 6f764b0c853..b06b1bf300b 100644
--- a/NEWS
+++ b/NEWS
@@ -11,6 +11,10 @@ PHP                                                                        NEWS
   . Fixed bug GH-19974 (fpm_status_export_to_zval segfault for parallel
     execution). (Jakub Zelenka, txuna)
 
+- GD:
+  . Fixed bug GH-20070 (Return type violation in imagefilter when an invalid
+    filter is provided). (Girgias)
+
 - Opcache:
   . Fixed bug GH-20081 (access to uninitialized vars in preload_load()).
     (Arnaud)
diff --git a/ext/gd/gd.c b/ext/gd/gd.c
index 44e46841062..2c3fce862ea 100644
--- a/ext/gd/gd.c
+++ b/ext/gd/gd.c
@@ -3404,9 +3404,11 @@ PHP_FUNCTION(imagefilter)
 		RETURN_THROWS();
 	}
 
-	if (filtertype >= 0 && filtertype <= IMAGE_FILTER_MAX) {
-		filters[filtertype](INTERNAL_FUNCTION_PARAM_PASSTHRU);
+	if (UNEXPECTED(filtertype < 0 || filtertype > IMAGE_FILTER_MAX)) {
+		zend_argument_value_error(2, "must be one of the IMG_FILTER_* filter constants");
+		RETURN_THROWS();
 	}
+	filters[filtertype](INTERNAL_FUNCTION_PARAM_PASSTHRU);
 }
 /* }}} */
 
diff --git a/ext/gd/tests/imagefilter_invalid_filter_error.phpt b/ext/gd/tests/imagefilter_invalid_filter_error.phpt
new file mode 100644
index 00000000000..f543e4a69f5
--- /dev/null
+++ b/ext/gd/tests/imagefilter_invalid_filter_error.phpt
@@ -0,0 +1,16 @@
+--TEST--
+GH-20070: Testing wrong parameter passing in imagefilter() of GD library
+--EXTENSIONS--
+gd
+--FILE--
+<?php
+$image = imagecreatetruecolor(1, 1);
+
+try {
+    var_dump(imagefilter($image, -1));
+} catch (Throwable $e) {
+    echo $e::class, ': ', $e->getMessage(), "\n";
+}
+?>
+--EXPECT--
+ValueError: imagefilter(): Argument #2 ($filter) must be one of the IMG_FILTER_* filter constants