diff --git a/ext/standard/array.c b/ext/standard/array.c
index d4e3742bb71f..a1a929340848 100644
--- a/ext/standard/array.c
+++ b/ext/standard/array.c
@@ -1029,11 +1029,50 @@ static inline HashTable *get_ht_for_iap(zval *zv, bool separate) {
 	return zobj->handlers->get_properties(zobj);
 }
 
+static zval *php_array_iter_seek_current(HashTable *array, bool forward_direction)
+{
+	zval *entry;
+
+	while (true) {
+		if ((entry = zend_hash_get_current_data(array)) == NULL) {
+			return NULL;
+		}
+
+		ZVAL_DEINDIRECT(entry);
+
+		/* Possible with an uninitialized typed property */
+		if (UNEXPECTED(Z_TYPE_P(entry) == IS_UNDEF)) {
+			zend_result result;
+			if (forward_direction) {
+				result = zend_hash_move_forward(array);
+			} else {
+				result = zend_hash_move_backwards(array);
+			}
+			if (result != SUCCESS) {
+				return NULL;
+			}
+		} else {
+			break;
+		}
+	}
+
+	return entry;
+}
+
+static void php_array_iter_return_current(zval *return_value, HashTable *array, bool forward_direction)
+{
+	zval *entry = php_array_iter_seek_current(array, forward_direction);
+	if (EXPECTED(entry)) {
+		RETURN_COPY_DEREF(entry);
+	} else {
+		RETURN_FALSE;
+	}
+}
+
 /* {{{ Advances array argument's internal pointer to the last element and return it */
 PHP_FUNCTION(end)
 {
 	zval *array_zv;
-	zval *entry;
 
 	ZEND_PARSE_PARAMETERS_START(1, 1)
 		Z_PARAM_ARRAY_OR_OBJECT_EX(array_zv, 0, 1)
@@ -1047,15 +1086,7 @@ PHP_FUNCTION(end)
 	zend_hash_internal_pointer_end(array);
 
 	if (USED_RET()) {
-		if ((entry = zend_hash_get_current_data(array)) == NULL) {
-			RETURN_FALSE;
-		}
-
-		if (Z_TYPE_P(entry) == IS_INDIRECT) {
-			entry = Z_INDIRECT_P(entry);
-		}
-
-		RETURN_COPY_DEREF(entry);
+		php_array_iter_return_current(return_value, array, false);
 	}
 }
 /* }}} */
@@ -1064,7 +1095,6 @@ PHP_FUNCTION(end)
 PHP_FUNCTION(prev)
 {
 	zval *array_zv;
-	zval *entry;
 
 	ZEND_PARSE_PARAMETERS_START(1, 1)
 		Z_PARAM_ARRAY_OR_OBJECT_EX(array_zv, 0, 1)
@@ -1078,15 +1108,7 @@ PHP_FUNCTION(prev)
 	zend_hash_move_backwards(array);
 
 	if (USED_RET()) {
-		if ((entry = zend_hash_get_current_data(array)) == NULL) {
-			RETURN_FALSE;
-		}
-
-		if (Z_TYPE_P(entry) == IS_INDIRECT) {
-			entry = Z_INDIRECT_P(entry);
-		}
-
-		RETURN_COPY_DEREF(entry);
+		php_array_iter_return_current(return_value, array, false);
 	}
 }
 /* }}} */
@@ -1095,7 +1117,6 @@ PHP_FUNCTION(prev)
 PHP_FUNCTION(next)
 {
 	zval *array_zv;
-	zval *entry;
 
 	ZEND_PARSE_PARAMETERS_START(1, 1)
 		Z_PARAM_ARRAY_OR_OBJECT_EX(array_zv, 0, 1)
@@ -1109,15 +1130,7 @@ PHP_FUNCTION(next)
 	zend_hash_move_forward(array);
 
 	if (USED_RET()) {
-		if ((entry = zend_hash_get_current_data(array)) == NULL) {
-			RETURN_FALSE;
-		}
-
-		if (Z_TYPE_P(entry) == IS_INDIRECT) {
-			entry = Z_INDIRECT_P(entry);
-		}
-
-		RETURN_COPY_DEREF(entry);
+		php_array_iter_return_current(return_value, array, true);
 	}
 }
 /* }}} */
@@ -1126,7 +1139,6 @@ PHP_FUNCTION(next)
 PHP_FUNCTION(reset)
 {
 	zval *array_zv;
-	zval *entry;
 
 	ZEND_PARSE_PARAMETERS_START(1, 1)
 		Z_PARAM_ARRAY_OR_OBJECT_EX(array_zv, 0, 1)
@@ -1140,15 +1152,7 @@ PHP_FUNCTION(reset)
 	zend_hash_internal_pointer_reset(array);
 
 	if (USED_RET()) {
-		if ((entry = zend_hash_get_current_data(array)) == NULL) {
-			RETURN_FALSE;
-		}
-
-		if (Z_TYPE_P(entry) == IS_INDIRECT) {
-			entry = Z_INDIRECT_P(entry);
-		}
-
-		RETURN_COPY_DEREF(entry);
+		php_array_iter_return_current(return_value, array, true);
 	}
 }
 /* }}} */
@@ -1157,22 +1161,13 @@ PHP_FUNCTION(reset)
 PHP_FUNCTION(current)
 {
 	zval *array_zv;
-	zval *entry;
 
 	ZEND_PARSE_PARAMETERS_START(1, 1)
 		Z_PARAM_ARRAY_OR_OBJECT(array_zv)
 	ZEND_PARSE_PARAMETERS_END();
 
 	HashTable *array = get_ht_for_iap(array_zv, /* separate */ false);
-	if ((entry = zend_hash_get_current_data(array)) == NULL) {
-		RETURN_FALSE;
-	}
-
-	if (Z_TYPE_P(entry) == IS_INDIRECT) {
-		entry = Z_INDIRECT_P(entry);
-	}
-
-	RETURN_COPY_DEREF(entry);
+	php_array_iter_return_current(return_value, array, true);
 }
 /* }}} */
 
@@ -1186,7 +1181,10 @@ PHP_FUNCTION(key)
 	ZEND_PARSE_PARAMETERS_END();
 
 	HashTable *array = get_ht_for_iap(array_zv, /* separate */ false);
-	zend_hash_get_current_key_zval(array, return_value);
+	zval *entry = php_array_iter_seek_current(array, true);
+	if (EXPECTED(entry)) {
+		zend_hash_get_current_key_zval(array, return_value);
+	}
 }
 /* }}} */
 
diff --git a/ext/standard/tests/array/gh16905.phpt b/ext/standard/tests/array/gh16905.phpt
new file mode 100644
index 000000000000..89d11575789e
--- /dev/null
+++ b/ext/standard/tests/array/gh16905.phpt
@@ -0,0 +1,92 @@
+--TEST--
+GH-16905 (Internal iterator functions can't handle UNDEF properties)
+--FILE--
+<?php
+
+class TestSomeUndef {
+	public int $a;
+	public int $b;
+	public int $c;
+	public int $d;
+}
+
+class TestAllUndef {
+	public int $a;
+}
+
+$x = new TestSomeUndef;
+$x->b = 1;
+$x->c = 2;
+
+var_dump(reset($x));
+var_dump(current($x));
+var_dump(end($x));
+
+var_dump(reset($x));
+var_dump(next($x));
+
+var_dump(end($x));
+var_dump(prev($x));
+
+var_dump(key($x));
+var_dump(current($x));
+
+$x = new TestAllUndef;
+var_dump(key($x));
+var_dump(current($x));
+
+$x->a = 1;
+var_dump(key($x));
+var_dump(current($x));
+reset($x);
+var_dump(key($x));
+var_dump(current($x));
+
+?>
+--EXPECTF--
+Deprecated: reset(): Calling reset() on an object is deprecated in %s on line %d
+int(1)
+
+Deprecated: current(): Calling current() on an object is deprecated in %s on line %d
+int(1)
+
+Deprecated: end(): Calling end() on an object is deprecated in %s on line %d
+int(2)
+
+Deprecated: reset(): Calling reset() on an object is deprecated in %s on line %d
+int(1)
+
+Deprecated: next(): Calling next() on an object is deprecated in %s on line %d
+int(2)
+
+Deprecated: end(): Calling end() on an object is deprecated in %s on line %d
+int(2)
+
+Deprecated: prev(): Calling prev() on an object is deprecated in %s on line %d
+int(1)
+
+Deprecated: key(): Calling key() on an object is deprecated in %s on line %d
+string(1) "b"
+
+Deprecated: current(): Calling current() on an object is deprecated in %s on line %d
+int(1)
+
+Deprecated: key(): Calling key() on an object is deprecated in %s on line %d
+NULL
+
+Deprecated: current(): Calling current() on an object is deprecated in %s on line %d
+bool(false)
+
+Deprecated: key(): Calling key() on an object is deprecated in %s on line %d
+NULL
+
+Deprecated: current(): Calling current() on an object is deprecated in %s on line %d
+bool(false)
+
+Deprecated: reset(): Calling reset() on an object is deprecated in %s on line %d
+
+Deprecated: key(): Calling key() on an object is deprecated in %s on line %d
+string(1) "a"
+
+Deprecated: current(): Calling current() on an object is deprecated in %s on line %d
+int(1)