diff --git a/Foundation/src/Thread_POSIX.cpp b/Foundation/src/Thread_POSIX.cpp
index c52fe2ce1..78459dabb 100644
--- a/Foundation/src/Thread_POSIX.cpp
+++ b/Foundation/src/Thread_POSIX.cpp
@@ -39,8 +39,10 @@
 #include "Poco/ErrorHandler.h"
 #include <signal.h>
 #if defined(__sun) && defined(__SVR4)
-#define __EXTENSIONS__
-#include <limits.h>
+#	if !defined(__EXTENSIONS__)
+#		define __EXTENSIONS__
+#	endif
+#	include <limits.h>
 #endif
 
 
@@ -151,14 +153,14 @@ int ThreadImpl::getMaxOSPriorityImpl()
 
 void ThreadImpl::setStackSizeImpl(int size)
 {
-#ifdef POCO_OS_CYGWIN
+#if (POCO_OS == POCO_OS_CYGWIN)
 	_pData->stackSize = 0;
 #else
  	if (size !=0 && size < PTHREAD_STACK_MIN)
  		size = PTHREAD_STACK_MIN;
 
  	_pData->stackSize = size;
-#endif
+#endif // (POCO_OS == POCO_OS_CYGWIN)
 }
 
 
diff --git a/Foundation/testsuite/src/ThreadTest.cpp b/Foundation/testsuite/src/ThreadTest.cpp
index d0bdf6432..6b76b530e 100644
--- a/Foundation/testsuite/src/ThreadTest.cpp
+++ b/Foundation/testsuite/src/ThreadTest.cpp
@@ -37,9 +37,10 @@
 #include "Poco/Runnable.h"
 #include "Poco/ThreadTarget.h"
 #include "Poco/Event.h"
-#include <iostream>
 #if defined(__sun) && defined(__SVR4)
-#define __EXTENSIONS__
+#	if !defined(__EXTENSIONS__)
+#		define __EXTENSIONS__
+#	endif
 #include <limits.h>
 #endif
 
@@ -281,7 +282,7 @@ void ThreadTest::testThreadStackSize()
 
 	stackSize = 1;
 	thread.setStackSize(stackSize);
-#if defined(POCO_OS_FAMILY_UNIX) && !defined(POCO_OS_CYGWIN)
+#if defined(POCO_OS_FAMILY_UNIX) && !(POCO_OS == POCO_OS_CYGWIN)
 	assert (PTHREAD_STACK_MIN == thread.getStackSize());
 #else
 	assert (stackSize == thread.getStackSize());