diff --git a/gnucash/import-export/log-replay/gnc-log-replay.cpp b/gnucash/import-export/log-replay/gnc-log-replay.cpp
index 63e7e0a41d..6685c59b0c 100644
--- a/gnucash/import-export/log-replay/gnc-log-replay.cpp
+++ b/gnucash/import-export/log-replay/gnc-log-replay.cpp
@@ -34,7 +34,7 @@
 
 #include "Account.h"
 #include "Transaction.h"
-#include "TransactionP.h"
+#include "TransactionP.hpp"
 #include "TransLog.h"
 #include "Scrub.h"
 #include "gnc-log-replay.h"
diff --git a/libgnucash/backend/xml/gnc-transaction-xml-v2.cpp b/libgnucash/backend/xml/gnc-transaction-xml-v2.cpp
index ecf3e40cbe..92ec28a5eb 100644
--- a/libgnucash/backend/xml/gnc-transaction-xml-v2.cpp
+++ b/libgnucash/backend/xml/gnc-transaction-xml-v2.cpp
@@ -27,7 +27,7 @@
 #include <string.h>
 #include "AccountP.hpp"
 #include "Transaction.h"
-#include "TransactionP.h"
+#include "TransactionP.hpp"
 #include "gnc-lot.h"
 #include "gnc-lot-p.h"
 
diff --git a/libgnucash/backend/xml/io-gncxml-v1.cpp b/libgnucash/backend/xml/io-gncxml-v1.cpp
index 789a72ff7a..0b008cf68e 100644
--- a/libgnucash/backend/xml/io-gncxml-v1.cpp
+++ b/libgnucash/backend/xml/io-gncxml-v1.cpp
@@ -38,7 +38,7 @@
 #include <Query.h>
 #include <Scrub.h>
 #include <Transaction.h>
-#include <TransactionP.h>
+#include <TransactionP.hpp>
 #include <TransLog.h>
 #include <gnc-pricedb.h>
 #include <gnc-pricedb-p.h>
diff --git a/libgnucash/backend/xml/io-gncxml-v2.cpp b/libgnucash/backend/xml/io-gncxml-v2.cpp
index 193fb7a544..76c562c616 100644
--- a/libgnucash/backend/xml/io-gncxml-v2.cpp
+++ b/libgnucash/backend/xml/io-gncxml-v2.cpp
@@ -51,7 +51,7 @@
 #include "SX-book.h"
 #include "SX-book-p.h"
 #include "Transaction.h"
-#include "TransactionP.h"
+#include "TransactionP.hpp"
 #include "TransLog.h"
 #if PLATFORM(WINDOWS)
 #ifdef __STRICT_ANSI_UNSET__
diff --git a/libgnucash/backend/xml/test/test-xml-transaction.cpp b/libgnucash/backend/xml/test/test-xml-transaction.cpp
index 39470ddbeb..b7ccfe2c54 100644
--- a/libgnucash/backend/xml/test/test-xml-transaction.cpp
+++ b/libgnucash/backend/xml/test/test-xml-transaction.cpp
@@ -42,7 +42,7 @@
 
 #include <AccountP.hpp>
 #include <Transaction.h>
-#include <TransactionP.h>
+#include <TransactionP.hpp>
 
 #include "../gnc-xml-helper.h"
 #include "../gnc-xml.h"
diff --git a/libgnucash/engine/Account.cpp b/libgnucash/engine/Account.cpp
index 2b45128148..f164e18720 100644
--- a/libgnucash/engine/Account.cpp
+++ b/libgnucash/engine/Account.cpp
@@ -37,7 +37,7 @@
 #include "Account.hpp"
 #include "Split.h"
 #include "Transaction.h"
-#include "TransactionP.h"
+#include "TransactionP.hpp"
 #include "gnc-event.h"
 #include "gnc-glib-utils.h"
 #include "gnc-lot.h"
diff --git a/libgnucash/engine/CMakeLists.txt b/libgnucash/engine/CMakeLists.txt
index dbd2516c9e..202d910254 100644
--- a/libgnucash/engine/CMakeLists.txt
+++ b/libgnucash/engine/CMakeLists.txt
@@ -9,7 +9,7 @@ set(engine_noinst_HEADERS
   SplitP.h
   SX-book.h
   SX-ttinfo.h
-  TransactionP.h
+  TransactionP.hpp
   gnc-backend-prov.hpp
   gnc-date-p.h
   gnc-int128.hpp
diff --git a/libgnucash/engine/Query.cpp b/libgnucash/engine/Query.cpp
index 16f45db6b3..38e9f4f77a 100644
--- a/libgnucash/engine/Query.cpp
+++ b/libgnucash/engine/Query.cpp
@@ -43,7 +43,7 @@
 #include "Account.h"
 #include "Query.h"
 #include "Transaction.h"
-#include "TransactionP.h"
+#include "TransactionP.hpp"
 
 static QofLogModule log_module = GNC_MOD_QUERY;
 
diff --git a/libgnucash/engine/Scrub.cpp b/libgnucash/engine/Scrub.cpp
index f468f13f76..b80113591d 100644
--- a/libgnucash/engine/Scrub.cpp
+++ b/libgnucash/engine/Scrub.cpp
@@ -50,7 +50,7 @@
 #include "Account.hpp"
 #include "Scrub.h"
 #include "Transaction.h"
-#include "TransactionP.h"
+#include "TransactionP.hpp"
 #include "gnc-commodity.h"
 #include "qofinstance-p.h"
 #include "gnc-session.h"
diff --git a/libgnucash/engine/Scrub2.cpp b/libgnucash/engine/Scrub2.cpp
index 265492f738..7c78bca4d7 100644
--- a/libgnucash/engine/Scrub2.cpp
+++ b/libgnucash/engine/Scrub2.cpp
@@ -39,7 +39,7 @@
 #include "AccountP.hpp"
 #include "Account.hpp"
 #include "Transaction.h"
-#include "TransactionP.h"
+#include "TransactionP.hpp"
 #include "Scrub2.h"
 #include "cap-gains.h"
 #include "gnc-engine.h"
diff --git a/libgnucash/engine/Scrub3.cpp b/libgnucash/engine/Scrub3.cpp
index 69bda2edc3..2572f4be79 100644
--- a/libgnucash/engine/Scrub3.cpp
+++ b/libgnucash/engine/Scrub3.cpp
@@ -43,7 +43,7 @@
 #include "Scrub2.h"
 #include "Scrub3.h"
 #include "Transaction.h"
-#include "TransactionP.h"
+#include "TransactionP.hpp"
 
 static QofLogModule log_module = GNC_MOD_LOT;
 
diff --git a/libgnucash/engine/Split.cpp b/libgnucash/engine/Split.cpp
index 85fa02fa52..d4c6baaa53 100644
--- a/libgnucash/engine/Split.cpp
+++ b/libgnucash/engine/Split.cpp
@@ -49,7 +49,7 @@
 #include "Split.h"
 #include "AccountP.hpp"
 #include "Scrub.h"
-#include "TransactionP.h"
+#include "TransactionP.hpp"
 #include "TransLog.h"
 #include "cap-gains.h"
 #include "gnc-commodity.h"
diff --git a/libgnucash/engine/TransLog.cpp b/libgnucash/engine/TransLog.cpp
index 151e9a2a79..2145d22c8a 100644
--- a/libgnucash/engine/TransLog.cpp
+++ b/libgnucash/engine/TransLog.cpp
@@ -32,7 +32,7 @@
 
 #include "Account.h"
 #include "Transaction.h"
-#include "TransactionP.h"
+#include "TransactionP.hpp"
 #include "TransLog.h"
 #include "qof.h"
 #ifdef _MSC_VER
diff --git a/libgnucash/engine/Transaction.cpp b/libgnucash/engine/Transaction.cpp
index bc17b5d18e..0cc0fcf4aa 100644
--- a/libgnucash/engine/Transaction.cpp
+++ b/libgnucash/engine/Transaction.cpp
@@ -45,7 +45,7 @@
 #include "AccountP.hpp"
 #include "Scrub.h"
 #include "Scrub3.h"
-#include "TransactionP.h"
+#include "TransactionP.hpp"
 #include "SplitP.h"
 #include "TransLog.h"
 #include "cap-gains.h"
diff --git a/libgnucash/engine/TransactionP.h b/libgnucash/engine/TransactionP.hpp
similarity index 98%
rename from libgnucash/engine/TransactionP.h
rename to libgnucash/engine/TransactionP.hpp
index 6493fe96a4..50a2d80a87 100644
--- a/libgnucash/engine/TransactionP.h
+++ b/libgnucash/engine/TransactionP.hpp
@@ -1,5 +1,5 @@
 /********************************************************************\
- * TransactionP.h -- private header for transaction & splits        *
+ * TransactionP.hpp -- private header for transaction & splits        *
  * Copyright (C) 1997 Robin D. Clark                                *
  * Copyright (C) 1997-2000 Linas Vepstas <linas@linas.org>          *
  * Copyright (C) 2000 Bill Gribble                                  *
@@ -25,7 +25,7 @@
 
 /*
  * FILE:
- * TransactionP.h
+ * TransactionP.hpp
  *
  * FUNCTION:
  * The is the *private* transaction header file.  Code outside of
@@ -52,10 +52,6 @@
 #include "SplitP.h"
 #include "qof.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 
 /** STRUCTS *********************************************************/
 /*
@@ -197,9 +193,5 @@ TransTestFunctions* _utest_trans_fill_functions (void);
 
 /*@}*/
 
-#ifdef __cplusplus
-}
-#endif
-
 
 #endif /* XACC_TRANSACTION_P_H */
diff --git a/libgnucash/engine/cap-gains.cpp b/libgnucash/engine/cap-gains.cpp
index 3c004c552b..e9b677ee7c 100644
--- a/libgnucash/engine/cap-gains.cpp
+++ b/libgnucash/engine/cap-gains.cpp
@@ -63,7 +63,7 @@ ToDo:
 #include "Scrub2.h"
 #include "Scrub3.h"
 #include "Transaction.h"
-#include "TransactionP.h"
+#include "TransactionP.hpp"
 #include "cap-gains.h"
 #include "gnc-engine.h"
 #include "engine-helpers.h"
diff --git a/libgnucash/engine/cashobjects.cpp b/libgnucash/engine/cashobjects.cpp
index ef6d0edd0b..e4e3cc61c8 100644
--- a/libgnucash/engine/cashobjects.cpp
+++ b/libgnucash/engine/cashobjects.cpp
@@ -30,7 +30,7 @@
 #include "cashobjects.h"
 #include "gnc-engine.h"
 #include "AccountP.hpp"
-#include "TransactionP.h"
+#include "TransactionP.hpp"
 #include "SchedXaction.h"
 #include "SX-book-p.h"
 #include "gnc-pricedb-p.h"
diff --git a/libgnucash/engine/gnc-engine.cpp b/libgnucash/engine/gnc-engine.cpp
index b912ea063b..6ea75fd01f 100644
--- a/libgnucash/engine/gnc-engine.cpp
+++ b/libgnucash/engine/gnc-engine.cpp
@@ -30,7 +30,7 @@
 #include "AccountP.hpp"
 #include "SX-book-p.h"
 #include "gnc-budget.h"
-#include "TransactionP.h"
+#include "TransactionP.hpp"
 #include "gnc-commodity.h"
 #include "gnc-pricedb-p.h"
 
diff --git a/libgnucash/engine/gnc-engine.h b/libgnucash/engine/gnc-engine.h
index 1f911f9405..af626821bd 100644
--- a/libgnucash/engine/gnc-engine.h
+++ b/libgnucash/engine/gnc-engine.h
@@ -142,7 +142,7 @@ typedef struct account_s             Account;
  * divided into.
  *
  * This is the typename for a split. The actual structure is defined
- * in the private header TransactionP.h, but no one outside the engine
+ * in the private header TransactionP.hpp, but no one outside the engine
  * should include that file. Instead, access that data only through
  * the functions in Transaction.h .*/
 typedef struct split_s               Split;
@@ -153,7 +153,7 @@ typedef struct split_s               Split;
  * divided into one or more Splits (usually two).
  *
  * This is the typename for a transaction. The actual structure is
- * defined in the private header TransactionP.h, but no one outside
+ * defined in the private header TransactionP.hpp, but no one outside
  * the engine should include that file. Instead, access that data only
  * through the functions in Transaction.h .*/
 typedef struct transaction_s         Transaction;
diff --git a/libgnucash/engine/gnc-lot.cpp b/libgnucash/engine/gnc-lot.cpp
index 8e6cb5ad45..1ee3eedf00 100644
--- a/libgnucash/engine/gnc-lot.cpp
+++ b/libgnucash/engine/gnc-lot.cpp
@@ -51,7 +51,7 @@
 #include "gnc-lot-p.h"
 #include "cap-gains.h"
 #include "Transaction.h"
-#include "TransactionP.h"
+#include "TransactionP.hpp"
 #include "gncInvoice.h"
 
 /* This static indicates the debugging module that this .o belongs to.  */
diff --git a/libgnucash/engine/mocks/gmock-Transaction.h b/libgnucash/engine/mocks/gmock-Transaction.h
index b0537ed50f..804307186b 100644
--- a/libgnucash/engine/mocks/gmock-Transaction.h
+++ b/libgnucash/engine/mocks/gmock-Transaction.h
@@ -4,7 +4,7 @@
 #include <gmock/gmock.h>
 
 #include <Transaction.h>
-#include <TransactionP.h>
+#include <TransactionP.hpp>
 
 #include "gmock-gobject.h"
 
diff --git a/libgnucash/engine/policy.cpp b/libgnucash/engine/policy.cpp
index 35febca6f4..f67cc9d822 100644
--- a/libgnucash/engine/policy.cpp
+++ b/libgnucash/engine/policy.cpp
@@ -36,7 +36,7 @@
 #include "Account.h"
 #include "Account.hpp"
 #include "Transaction.h"
-#include "TransactionP.h"
+#include "TransactionP.hpp"
 #include "cap-gains.h"
 #include "gnc-engine.h"
 #include "gnc-lot.h"
diff --git a/libgnucash/engine/test-core/test-engine-stuff.cpp b/libgnucash/engine/test-core/test-engine-stuff.cpp
index 2024f8fb9a..8dbb440ece 100644
--- a/libgnucash/engine/test-core/test-engine-stuff.cpp
+++ b/libgnucash/engine/test-core/test-engine-stuff.cpp
@@ -62,7 +62,7 @@
 #include "gnc-engine.h"
 #include "gnc-session.h"
 #include "Transaction.h"
-#include "TransactionP.h"
+#include "TransactionP.hpp"
 #include "Recurrence.h"
 #include "SchedXaction.h"
 #include "SX-book.h"
diff --git a/libgnucash/engine/test/utest-Split.cpp b/libgnucash/engine/test/utest-Split.cpp
index 9293d79ee1..23d163ee59 100644
--- a/libgnucash/engine/test/utest-Split.cpp
+++ b/libgnucash/engine/test/utest-Split.cpp
@@ -31,7 +31,7 @@
 #include <SplitP.h>
 #include <Account.h>
 #include <Transaction.h>
-#include <TransactionP.h>
+#include <TransactionP.hpp>
 #include <gnc-lot.h>
 #include <gnc-event.h>
 
diff --git a/libgnucash/engine/test/utest-Transaction.cpp b/libgnucash/engine/test/utest-Transaction.cpp
index 704af204c9..5c252e5136 100644
--- a/libgnucash/engine/test/utest-Transaction.cpp
+++ b/libgnucash/engine/test/utest-Transaction.cpp
@@ -28,7 +28,7 @@
 #include <unittest-support.h>
 /* Add specific headers for this class */
 #include "../Transaction.h"
-#include "../TransactionP.h"
+#include "../TransactionP.hpp"
 #include "../Split.h"
 #include "../Account.h"
 #include "../gnc-lot.h"