diff --git a/src/bson-encode.c b/src/bson-encode.c
index 5f22d67c8..70524084d 100644
--- a/src/bson-encode.c
+++ b/src/bson-encode.c
@@ -401,6 +401,11 @@ void php_phongo_zval_to_bson(zval *data, php_phongo_bson_flags_t flags, bson_t *
 	 * properties, we'll need to filter them out later. */
 	bool         ht_data_from_properties = false;
 
+	/* If the object is an instance of MongoDB\BSON\Persistable, we will need to
+	 * inject the PHP class name as a BSON key and ignore any existing key in
+	 * the return value of bsonSerialize(). */
+	bool         skip_odm_field = false;
+
 	ZVAL_UNDEF(&obj_data);
 
 	switch(Z_TYPE_P(data)) {
@@ -455,11 +460,12 @@ void php_phongo_zval_to_bson(zval *data, php_phongo_bson_flags_t flags, bson_t *
 				if (instanceof_function(Z_OBJCE_P(data), php_phongo_persistable_ce TSRMLS_CC)) {
 #if PHP_VERSION_ID >= 70000
 					bson_append_binary(bson, PHONGO_ODM_FIELD_NAME, -1, 0x80, (const uint8_t *)Z_OBJCE_P(data)->name->val, Z_OBJCE_P(data)->name->len);
-					zend_hash_str_del(ht_data, PHONGO_ODM_FIELD_NAME, sizeof(PHONGO_ODM_FIELD_NAME)-1);
 #else
 					bson_append_binary(bson, PHONGO_ODM_FIELD_NAME, -1, 0x80, (const uint8_t *)Z_OBJCE_P(data)->name, strlen(Z_OBJCE_P(data)->name));
-					zend_hash_del(ht_data, PHONGO_ODM_FIELD_NAME, sizeof(PHONGO_ODM_FIELD_NAME));
 #endif
+					/* Ensure that we ignore an existing key with the same name
+					 * if one exists in the bsonSerialize() return value. */
+					skip_odm_field = true;
 				}
 
 				break;
@@ -504,6 +510,10 @@ void php_phongo_zval_to_bson(zval *data, php_phongo_bson_flags_t flags, bson_t *
 					goto cleanup;
 				}
 
+				if (skip_odm_field && !strcmp(ZSTR_VAL(string_key), PHONGO_ODM_FIELD_NAME)) {
+					continue;
+				}
+
 				if (flags & PHONGO_BSON_ADD_ID) {
 					if (!strcmp(ZSTR_VAL(string_key), "_id")) {
 						flags &= ~PHONGO_BSON_ADD_ID;
@@ -556,6 +566,10 @@ void php_phongo_zval_to_bson(zval *data, php_phongo_bson_flags_t flags, bson_t *
 				goto cleanup;
 			}
 
+			if (skip_odm_field && !strcmp(string_key, PHONGO_ODM_FIELD_NAME)) {
+				continue;
+			}
+
 			if (flags & PHONGO_BSON_ADD_ID) {
 				if (!strcmp(string_key, "_id")) {
 					flags &= ~PHONGO_BSON_ADD_ID;
diff --git a/tests/bson/bug1006-001.phpt b/tests/bson/bug1006-001.phpt
new file mode 100644
index 000000000..b57bf2c64
--- /dev/null
+++ b/tests/bson/bug1006-001.phpt
@@ -0,0 +1,54 @@
+--TEST--
+PHPC-1005: Do not modify memory of Persistable::bsonSerialize() return value
+--FILE--
+<?php
+
+require_once __DIR__ . '/../utils/tools.php';
+
+class MyClass implements MongoDB\BSON\Persistable
+{
+    public $data;
+
+    public function __construct()
+    {
+        $this->data = [
+            '__pclass' => 'baz',
+            'foo' => 'bar',
+        ];
+    }
+
+    function bsonSerialize()
+    {
+        return $this->data;
+    }
+
+    function bsonUnserialize(array $data)
+    {
+    }
+}
+
+$obj = new MyClass;
+var_dump($obj->data);
+hex_dump(fromPHP($obj));
+var_dump($obj->data);
+
+?>
+===DONE===
+<?php exit(0); ?>
+--EXPECT--
+array(2) {
+  ["__pclass"]=>
+  string(3) "baz"
+  ["foo"]=>
+  string(3) "bar"
+}
+     0 : 28 00 00 00 05 5f 5f 70 63 6c 61 73 73 00 07 00  [(....__pclass...]
+    10 : 00 00 80 4d 79 43 6c 61 73 73 02 66 6f 6f 00 04  [...MyClass.foo..]
+    20 : 00 00 00 62 61 72 00 00                          [...bar..]
+array(2) {
+  ["__pclass"]=>
+  string(3) "baz"
+  ["foo"]=>
+  string(3) "bar"
+}
+===DONE===