diff --git a/src/core_io.h b/src/core_io.h
--- a/src/core_io.h
+++ b/src/core_io.h
@@ -9,9 +9,9 @@
 #include <vector>
 
 class CBlock;
+class CMutableTransaction;
 class CScript;
 class CTransaction;
-struct CMutableTransaction;
 class uint256;
 class UniValue;
 
diff --git a/src/primitives/transaction.h b/src/primitives/transaction.h
--- a/src/primitives/transaction.h
+++ b/src/primitives/transaction.h
@@ -182,7 +182,7 @@
     std::string ToString() const;
 };
 
-struct CMutableTransaction;
+class CMutableTransaction;
 
 /**
  * Basic transaction serialization format:
@@ -302,8 +302,11 @@
     std::string ToString() const;
 };
 
-/** A mutable version of CTransaction. */
-struct CMutableTransaction {
+/**
+ * A mutable version of CTransaction.
+ */
+class CMutableTransaction {
+public:
     int32_t nVersion;
     std::vector<CTxIn> vin;
     std::vector<CTxOut> vout;
diff --git a/src/script/sign.h b/src/script/sign.h
--- a/src/script/sign.h
+++ b/src/script/sign.h
@@ -10,11 +10,10 @@
 
 class CKeyID;
 class CKeyStore;
+class CMutableTransaction;
 class CScript;
 class CTransaction;
 
-struct CMutableTransaction;
-
 /** Virtual base class for signature creators. */
 class BaseSignatureCreator {
 protected:
diff --git a/src/test/test_bitcoin.h b/src/test/test_bitcoin.h
--- a/src/test/test_bitcoin.h
+++ b/src/test/test_bitcoin.h
@@ -39,7 +39,7 @@
 };
 
 class CBlock;
-struct CMutableTransaction;
+class CMutableTransaction;
 class CScript;
 
 //