diff --git a/include/rapidjson/writer.h b/include/rapidjson/writer.h
index dc41a1b..02d6680 100644
--- a/include/rapidjson/writer.h
+++ b/include/rapidjson/writer.h
@@ -62,9 +62,11 @@ public:
         \param stackAllocator User supplied allocator. If it is null, it will create a private one.
         \param levelDepth Initial capacity of stack.
     */
+    explicit
     Writer(OutputStream& os, StackAllocator* stackAllocator = 0, size_t levelDepth = kDefaultLevelDepth) : 
         os_(&os), level_stack_(stackAllocator, levelDepth * sizeof(Level)), hasRoot_(false) {}
 
+    explicit
     Writer(StackAllocator* allocator = 0, size_t levelDepth = kDefaultLevelDepth) :
         os_(0), level_stack_(allocator, levelDepth * sizeof(Level)), hasRoot_(false) {}