diff --git a/libs/ardour/convolver.cc b/libs/ardour/convolver.cc
index bd00dccbe5..d0caa8e669 100644
--- a/libs/ardour/convolver.cc
+++ b/libs/ardour/convolver.cc
@@ -34,6 +34,8 @@
 using namespace ARDOUR::DSP;
 using namespace ArdourZita;
 
+using ARDOUR::Session;
+
 Convolver::Convolver (Session& session, std::string const& path, IRChannelConfig irc, uint32_t pre_delay)
 	: SessionHandleRef (session)
 	, _irc (irc)
diff --git a/libs/zita-convolver/zita-convolver.cc b/libs/zita-convolver/zita-convolver.cc
index 91637b46d4..eb7d6603e1 100644
--- a/libs/zita-convolver/zita-convolver.cc
+++ b/libs/zita-convolver/zita-convolver.cc
@@ -22,8 +22,8 @@
 #include <string.h>
 #include <unistd.h>
 
-#if _MSC_VER
-#include <windows.h> // Needed for 'Sleep()'
+#ifdef _MSC_VER
+#include <windows.h>  // Needed for MSVC 'Sleep()'
 #endif
 
 #include "zita-convolver/zita-convolver.h"
@@ -356,7 +356,7 @@ Convproc::cleanup (void)
 	uint32_t k;
 
 	while (!check_stop ()) {
-#if _MSC_VER
+#ifdef _MSC_VER
 		Sleep (100);
 #else
 		usleep (100000);
diff --git a/libs/zita-convolver/zita-convolver/zita-convolver.h b/libs/zita-convolver/zita-convolver/zita-convolver.h
index 39ec4ed474..6c4859bce5 100644
--- a/libs/zita-convolver/zita-convolver/zita-convolver.h
+++ b/libs/zita-convolver/zita-convolver/zita-convolver.h
@@ -20,6 +20,7 @@
 #ifndef ARDOUR_ZITA_CONVOLVER_H
 #define ARDOUR_ZITA_CONVOLVER_H
 
+
 #include <fftw3.h>
 #include <pthread.h>
 #include <stdint.h>
@@ -32,11 +33,8 @@ namespace ArdourZita {
 #undef ZCSEMA_IS_IMPLEMENTED
 #endif
 
-/* Note:
- * - __MINGW32__ is also defined for 64bit builds
- * - mingw, x-compile uses PTW32's implementation of semaphores, we should prefer defined(PTW32_VERSION)
- */
-#if defined(__linux__) || defined(__GNU__) || defined(__FreeBSD__) || defined(__FreeBSD_kernel__) || defined (__MINGW32__)
+/* note: mingw and msvc actually use PTW32's implementation of semaphores */
+#if defined(__linux__) || defined(__GNU__) || defined(__FreeBSD__) || defined(__FreeBSD_kernel__) || defined(PTW32_VERSION)
 
 #include <semaphore.h>
 
@@ -53,9 +51,6 @@ public:
 		sem_destroy (&_sema);
 	}
 
-	ZCsema (const ZCsema&);            // disabled
-	ZCsema& operator= (const ZCsema&); // disabled
-
 	int init (int s, int v)
 	{
 		return sem_init (&_sema, s, v);
@@ -77,13 +72,15 @@ public:
 	}
 
 private:
+	ZCsema (const ZCsema&);            // disabled
+	ZCsema& operator= (const ZCsema&); // disabled
+
 	sem_t _sema;
 };
 
 #define ZCSEMA_IS_IMPLEMENTED
-#endif
 
-#if defined (__APPLE__) || defined (_MSC_VER)
+#elif defined (__APPLE__)
 
 // NOTE:  ***** I DO NOT REPEAT NOT PROVIDE SUPPORT FOR OSX *****
 //
@@ -106,10 +103,8 @@ public:
 		pthread_cond_destroy (&_cond);
 	}
 
-#ifndef _MSC_VER /* remove for MSVC build */
 	ZCsema (const ZCsema&);            // disabled
 	ZCsema& operator= (const ZCsema&); // disabled
-#endif
 
 	int init (int s, int v)
 	{