diff --git a/lib/php/src/ext/thrift_protocol/php_thrift_protocol7.cpp b/lib/php/src/ext/thrift_protocol/php_thrift_protocol7.cpp
index d5a2eaf..59fa30a 100644
--- a/lib/php/src/ext/thrift_protocol/php_thrift_protocol7.cpp
+++ b/lib/php/src/ext/thrift_protocol/php_thrift_protocol7.cpp
@@ -626,7 +626,7 @@
 
       for (uint32_t s = 0; s < size; ++s) {
         zval key, value;
-        ZVAL_UNDEF(&value);
+        ZVAL_TRUE(&value);
 
         binary_deserialize(type, transport, &key, elemspec);