diff --git a/include/rapidjson/schema.h b/include/rapidjson/schema.h
index 26ae947..1ff8883 100644
--- a/include/rapidjson/schema.h
+++ b/include/rapidjson/schema.h
@@ -899,7 +899,7 @@ public:
                 }
         }
 
-        SizeType index;
+        SizeType index  = 0;
         if (FindPropertyIndex(ValueType(str, len).Move(), &index)) {
             if (context.patternPropertiesSchemaCount > 0) {
                 context.patternPropertiesSchemas[context.patternPropertiesSchemaCount++] = properties_[index].schema;