diff --git a/php/src/Google/Protobuf/Internal/Descriptor.php b/php/src/Google/Protobuf/Internal/Descriptor.php
index 02b543329011a..a7f80d534e01e 100644
--- a/php/src/Google/Protobuf/Internal/Descriptor.php
+++ b/php/src/Google/Protobuf/Internal/Descriptor.php
@@ -193,6 +193,10 @@ public static function buildFromProto($proto, $file_proto, $containing)
         $desc->setLegacyClass($legacy_classname);
         $desc->setOptions($proto->getOptions());
 
+        foreach ($proto->getField() as $field_proto) {
+            $desc->addField(FieldDescriptor::buildFromProto($field_proto));
+        }
+
         // Handle nested types.
         foreach ($proto->getNestedType() as $nested_proto) {
             $desc->addNestedType(Descriptor::buildFromProto(
@@ -213,11 +217,6 @@ public static function buildFromProto($proto, $file_proto, $containing)
             $index++;
         }
 
-        // Pass the descriptor to build FieldDescriptor after the OneofDescriptors are populated.
-        foreach ($proto->getField() as $field_proto) {
-            $desc->addField(FieldDescriptor::buildFromProto($field_proto, $desc));
-        }
-
         return $desc;
     }
 }
diff --git a/php/src/Google/Protobuf/Internal/FieldDescriptor.php b/php/src/Google/Protobuf/Internal/FieldDescriptor.php
index 875280b75ca66..3a9a73b729ff9 100644
--- a/php/src/Google/Protobuf/Internal/FieldDescriptor.php
+++ b/php/src/Google/Protobuf/Internal/FieldDescriptor.php
@@ -187,6 +187,11 @@ public function getContainingOneof()
         return $this->containing_oneof;
     }
 
+    public function setContainingOneof($containing_oneof)
+    {
+        $this->containing_oneof = $containing_oneof;
+    }
+
     public function getRealContainingOneof()
     {
         return !is_null($this->containing_oneof) && !$this->containing_oneof->isSynthetic()
@@ -240,10 +245,9 @@ private static function isTypePackable($field_type)
 
     /**
      * @param FieldDescriptorProto $proto
-     * @param Descriptor $desc
      * @return FieldDescriptor
      */
-    public static function getFieldDescriptor($proto, $desc)
+    public static function getFieldDescriptor($proto)
     {
         $type_name = null;
         $type = $proto->getType();
@@ -257,13 +261,7 @@ public static function getFieldDescriptor($proto, $desc)
                 break;
         }
 
-        if ($proto->hasOneofIndex()) {
-            $oneof_index = $proto->getOneofIndex();
-            $containing_oneof = $desc->getOneofDecl()[$oneof_index];
-        } else {
-            $oneof_index = -1;
-            $containing_oneof = null;
-        }
+        $oneof_index = $proto->hasOneofIndex() ? $proto->getOneofIndex() : -1;
         // TODO: once proto2 is supported, this default should be false
         // for proto2.
         if ($proto->getLabel() === GPBLabel::REPEATED &&
@@ -282,10 +280,7 @@ public static function getFieldDescriptor($proto, $desc)
 
         $field = new FieldDescriptor();
         $field->setName($proto->getName());
-        $field->containing_oneof = $containing_oneof;
 
-        $json_name = $proto->hasJsonName() ? $proto->getJsonName() :
-            lcfirst(implode('', array_map('ucwords', explode('_', $proto->getName()))));
         if ($proto->hasJsonName()) {
             $json_name = $proto->getJsonName();
         } else {
@@ -324,8 +319,8 @@ public static function getFieldDescriptor($proto, $desc)
         return $field;
     }
 
-    public static function buildFromProto($proto, $parent_desc)
+    public static function buildFromProto($proto)
     {
-        return FieldDescriptor::getFieldDescriptor($proto, $parent_desc);
+        return FieldDescriptor::getFieldDescriptor($proto);
     }
 }
diff --git a/php/src/Google/Protobuf/Internal/OneofDescriptor.php b/php/src/Google/Protobuf/Internal/OneofDescriptor.php
index a74be1e58518a..9c8a8ed7f20b7 100644
--- a/php/src/Google/Protobuf/Internal/OneofDescriptor.php
+++ b/php/src/Google/Protobuf/Internal/OneofDescriptor.php
@@ -76,10 +76,13 @@ public static function buildFromProto($oneof_proto, $desc, $index)
         $oneof = new OneofDescriptor();
         $oneof->setName($oneof_proto->getName());
         foreach ($desc->getField() as $field) {
+            /** @var FieldDescriptor $field */
             if ($field->getOneofIndex() == $index) {
                 $oneof->addField($field);
+                $field->setContainingOneof($oneof);
             }
         }
+
         return $oneof;
     }
 }
diff --git a/php/src/Google/Protobuf/OneofDescriptor.php b/php/src/Google/Protobuf/OneofDescriptor.php
index 9717da8a77f18..66ffbd5caf9d5 100644
--- a/php/src/Google/Protobuf/OneofDescriptor.php
+++ b/php/src/Google/Protobuf/OneofDescriptor.php
@@ -63,6 +63,12 @@ public function getName()
      */
     public function getField($index)
     {
+        if (
+            is_null($this->internal_desc->getFields())
+            || !isset($this->internal_desc->getFields()[$index])
+        ) {
+            return null;
+        }
         return $this->getPublicDescriptor($this->internal_desc->getFields()[$index]);
     }