diff --git a/Utilities/kwsys/CMakeLists.txt b/Utilities/kwsys/CMakeLists.txt
index 5e725e41a2b..083629ac32c 100644
--- a/Utilities/kwsys/CMakeLists.txt
+++ b/Utilities/kwsys/CMakeLists.txt
@@ -601,6 +601,14 @@ ENDIF(KWSYS_BUILD_SHARED)
 #-----------------------------------------------------------------------------
 # Configure some implementation details.
 
+KWSYS_PLATFORM_C_TEST(KWSYS_C_HAS_PTRDIFF_T
+  "Checking whether C compiler has ptrdiff_t in stddef.h" DIRECT)
+KWSYS_PLATFORM_C_TEST(KWSYS_C_HAS_SSIZE_T
+  "Checking whether C compiler has ssize_t in unistd.h" DIRECT)
+SET_SOURCE_FILES_PROPERTIES(ProcessUNIX.c System.c PROPERTIES
+  COMPILE_FLAGS "-DKWSYS_C_HAS_PTRDIFF_T=${KWSYS_C_HAS_PTRDIFF_T} -DKWSYS_C_HAS_SSIZE_T=${KWSYS_C_HAS_SSIZE_T}"
+  )
+
 IF(KWSYS_DO_NOT_CLEAN_PUTENV)
   # Disable cleanup of putenv memory for issues with GCOV.
   SET_SOURCE_FILES_PROPERTIES(SystemTools.cxx PROPERTIES
@@ -785,15 +793,6 @@ IF(KWSYS_USE_Process)
   ELSE(NOT UNIX)
     # Use the UNIX implementation.
     SET(KWSYS_C_SRCS ${KWSYS_C_SRCS} ProcessUNIX.c)
-
-    # Help ProcessUNIX.c compile properly on all platforms.
-    KWSYS_PLATFORM_C_TEST(KWSYS_C_HAS_PTRDIFF_T
-      "Checking whether C compiler has ptrdiff_t in stddef.h" DIRECT)
-    KWSYS_PLATFORM_C_TEST(KWSYS_C_HAS_SSIZE_T
-      "Checking whether C compiler has ssize_t in unistd.h" DIRECT)
-    SET_SOURCE_FILES_PROPERTIES(ProcessUNIX.c PROPERTIES
-      COMPILE_FLAGS "-DKWSYS_C_HAS_PTRDIFF_T=${KWSYS_C_HAS_PTRDIFF_T} -DKWSYS_C_HAS_SSIZE_T=${KWSYS_C_HAS_SSIZE_T}"
-      )
   ENDIF(NOT UNIX)
 ENDIF(KWSYS_USE_Process)