diff --git a/src/core_io.h b/src/core_io.h
index 4344290bb88..88425ed4fbd 100644
--- a/src/core_io.h
+++ b/src/core_io.h
@@ -11,7 +11,7 @@
 class CBlock;
 class CScript;
 class CTransaction;
-class CMutableTransaction;
+struct CMutableTransaction;
 class uint256;
 class UniValue;