diff --git a/js/src/assembler/assembler/LinkBuffer.h b/js/src/assembler/assembler/LinkBuffer.h
index 8107291205c..b0a611b168d 100644
--- a/js/src/assembler/assembler/LinkBuffer.h
+++ b/js/src/assembler/assembler/LinkBuffer.h
@@ -77,7 +77,9 @@ public:
         : m_executablePool(NULL)
         , m_code(ncode)
         , m_size(size)
+#ifndef NDEBUG
         , m_completed(false)
+#endif
     {
     }