diff --git a/ext/intl/resourcebundle/resourcebundle_iterator.c b/ext/intl/resourcebundle/resourcebundle_iterator.c
index 9ec97f64f51d4..7d8d21a61fbab 100644
--- a/ext/intl/resourcebundle/resourcebundle_iterator.c
+++ b/ext/intl/resourcebundle/resourcebundle_iterator.c
@@ -29,10 +29,17 @@
 /* {{{ resourcebundle_iterator_read */
 static void resourcebundle_iterator_read( ResourceBundle_iterator *iterator )
 {
-	UErrorCode icuerror = U_ZERO_ERROR;
+	UErrorCode icuerror;
 	ResourceBundle_object *rb = iterator->subject;
 
-	rb->child = ures_getByIndex( rb->me, iterator->i, rb->child, &icuerror );
+	ZEND_ASSERT(Z_ISUNDEF(iterator->current));
+
+	/* Skip non-existing resource entries in the bundle, similar to how holes in arrays are skipped
+	 * in foreach loops. See also GH-17317. */
+	do {
+		icuerror = U_ZERO_ERROR;
+		rb->child = ures_getByIndex( rb->me, iterator->i, rb->child, &icuerror );
+	} while (icuerror == U_MISSING_RESOURCE_ERROR && iterator->i++ < iterator->length);
 
 	if (U_SUCCESS(icuerror)) {
 		/* ATTN: key extraction must be the first thing to do... rb->child might be reset in read! */
@@ -43,7 +50,6 @@ static void resourcebundle_iterator_read( ResourceBundle_iterator *iterator )
 	}
 	else {
 		// zend_throw_exception( spl_ce_OutOfRangeException, "Running past end of ResourceBundle", 0);
-		ZVAL_UNDEF(&iterator->current);
 	}
 }
 /* }}} */
@@ -89,7 +95,7 @@ static zval *resourcebundle_iterator_current( zend_object_iterator *iter )
 {
 	ResourceBundle_iterator *iterator = (ResourceBundle_iterator *) iter;
 	if (Z_ISUNDEF(iterator->current)) {
-		resourcebundle_iterator_read( iterator);
+		return NULL;
 	}
 	return &iterator->current;
 }
@@ -100,9 +106,7 @@ static void resourcebundle_iterator_key( zend_object_iterator *iter, zval *key )
 {
 	ResourceBundle_iterator *iterator = (ResourceBundle_iterator *) iter;
 
-	if (Z_ISUNDEF(iterator->current)) {
-		resourcebundle_iterator_read( iterator);
-	}
+	ZEND_ASSERT(!Z_ISUNDEF(iterator->current));
 
 	if (iterator->is_table) {
 		ZVAL_STRING(key, iterator->currentkey);
@@ -119,6 +123,7 @@ static void resourcebundle_iterator_step( zend_object_iterator *iter )
 
 	iterator->i++;
 	resourcebundle_iterator_invalidate( iter );
+	resourcebundle_iterator_read(iterator);
 }
 /* }}} */
 
@@ -129,6 +134,7 @@ static void resourcebundle_iterator_reset( zend_object_iterator *iter )
 
 	iterator->i = 0;
 	resourcebundle_iterator_invalidate( iter );
+	resourcebundle_iterator_read(iterator);
 }
 /* }}} */
 
diff --git a/ext/intl/tests/gh17319.phpt b/ext/intl/tests/gh17319.phpt
new file mode 100644
index 0000000000000..7ed0c1eed3702
--- /dev/null
+++ b/ext/intl/tests/gh17319.phpt
@@ -0,0 +1,63 @@
+--TEST--
+GH-17319 (ResourceBundle iterator crash on NULL key)
+--EXTENSIONS--
+intl
+--CREDITS--
+KidFlo
+--FILE--
+<?php
+
+foreach ((new ResourceBundle('', NULL))->get('calendar')->get('buddhist') as $key => $value) {
+	echo "KEY: "; var_dump($key);
+	echo "VALUE: "; var_dump($value);
+}
+
+$bundle = (new ResourceBundle('', NULL))->get('calendar')->get('buddhist');
+$iterator = $bundle->getIterator();
+while ($iterator->valid()) {
+	var_dump($iterator->key());
+	$iterator->next();
+}
+
+?>
+--EXPECT--
+KEY: string(15) "AmPmMarkersAbbr"
+VALUE: object(ResourceBundle)#3 (0) {
+}
+KEY: string(15) "AmPmMarkersAbbr"
+VALUE: object(ResourceBundle)#4 (0) {
+}
+KEY: string(16) "DateTimePatterns"
+VALUE: object(ResourceBundle)#3 (0) {
+}
+KEY: string(11) "appendItems"
+VALUE: object(ResourceBundle)#4 (0) {
+}
+KEY: string(16) "availableFormats"
+VALUE: object(ResourceBundle)#3 (0) {
+}
+KEY: string(8) "dayNames"
+VALUE: object(ResourceBundle)#4 (0) {
+}
+KEY: string(4) "eras"
+VALUE: object(ResourceBundle)#3 (0) {
+}
+KEY: string(15) "intervalFormats"
+VALUE: object(ResourceBundle)#4 (0) {
+}
+KEY: string(10) "monthNames"
+VALUE: object(ResourceBundle)#3 (0) {
+}
+KEY: string(8) "quarters"
+VALUE: object(ResourceBundle)#4 (0) {
+}
+string(15) "AmPmMarkersAbbr"
+string(15) "AmPmMarkersAbbr"
+string(16) "DateTimePatterns"
+string(11) "appendItems"
+string(16) "availableFormats"
+string(8) "dayNames"
+string(4) "eras"
+string(15) "intervalFormats"
+string(10) "monthNames"
+string(8) "quarters"