diff --git a/src/primitives/transaction.h b/src/primitives/transaction.h
index c88d5b1ad..f6f8e3136 100644
--- a/src/primitives/transaction.h
+++ b/src/primitives/transaction.h
@@ -298,7 +298,7 @@ public:
     CTransaction();
 
     /** Convert a CMutableTransaction into a CTransaction. */
-    CTransaction(const CMutableTransaction &tx);
+    explicit CTransaction(const CMutableTransaction &tx);
     CTransaction(CMutableTransaction &&tx);
 
     template <typename Stream>