diff --git a/debuggerd/test/BacktraceMock.h b/debuggerd/test/BacktraceMock.h
index f75534e..6104f7e 100644
--- a/debuggerd/test/BacktraceMock.h
+++ b/debuggerd/test/BacktraceMock.h
@@ -41,7 +41,7 @@
 
 class BacktraceMock : public Backtrace {
  public:
-  BacktraceMock(BacktraceMapMock* map) : Backtrace(0, 0, map) {
+  explicit BacktraceMock(BacktraceMapMock* map) : Backtrace(0, 0, map) {
     if (map_ == nullptr) {
       abort();
     }