diff --git a/compiler/llvm/md_builder.h b/compiler/llvm/md_builder.h
index cc169a3..65c52c9 100644
--- a/compiler/llvm/md_builder.h
+++ b/compiler/llvm/md_builder.h
@@ -35,7 +35,7 @@
 
 class MDBuilder : public LLVMMDBuilder {
  public:
-  MDBuilder(::llvm::LLVMContext& context)
+  explicit MDBuilder(::llvm::LLVMContext& context)
      : LLVMMDBuilder(context), tbaa_root_(createTBAARoot("Art TBAA Root")) {
     std::memset(tbaa_special_type_, 0, sizeof(tbaa_special_type_));
     std::memset(tbaa_memory_jtype_, 0, sizeof(tbaa_memory_jtype_));