diff --git a/runtime/atomic_integer.h b/runtime/atomic_integer.h
index 57836d6..117e837 100644
--- a/runtime/atomic_integer.h
+++ b/runtime/atomic_integer.h
@@ -26,7 +26,7 @@
  public:
   AtomicInteger() : value_(0) { }
 
-  AtomicInteger(int32_t value) : value_(value) { }
+  explicit AtomicInteger(int32_t value) : value_(value) { }
 
   // Unsafe = operator for non atomic operations on the integer.
   AtomicInteger& operator = (int32_t new_value) {