diff --git a/Foundation/testsuite/src/ThreadTest.cpp b/Foundation/testsuite/src/ThreadTest.cpp
index 6a1491f78..fa78318e8 100644
--- a/Foundation/testsuite/src/ThreadTest.cpp
+++ b/Foundation/testsuite/src/ThreadTest.cpp
@@ -39,7 +39,9 @@
 #include "Poco/Event.h"
 #include <iostream>
 #if defined(__sun) && defined(__SVR4)
-#define __EXTENSIONS__
+#	if !defined(__EXTENSIONS__)
+#		define __EXTENSIONS__
+#	endif
 #endif
 #include <climits>
 
diff --git a/build/config/SunOS-SunStudio b/build/config/SunOS-SunStudio
index 84ac57a31..f71bddb6f 100755
--- a/build/config/SunOS-SunStudio
+++ b/build/config/SunOS-SunStudio
@@ -62,7 +62,7 @@ RELEASEOPT_LINK =
 #
 # System Specific Flags
 #
-SYSFLAGS = -D_REENTRANT -D_THREAD_SAFE -D_POSIX_PTHREAD_SEMANTICS
+SYSFLAGS = -D_REENTRANT -D_THREAD_SAFE -D_POSIX_PTHREAD_SEMANTICS -D_POSIX_C_SOURCE=199506L -D__EXTENSIONS__
 
 #
 # System Specific Libraries