diff --git a/config/check_depend.cmake b/config/check_depend.cmake
index 20ed2e5..779e987 100644
--- a/config/check_depend.cmake
+++ b/config/check_depend.cmake
@@ -195,7 +195,7 @@ if(OROCOS_TARGET STREQUAL "win32")
     set(CMAKE_LD_FLAGS_ADD "-Wl,--enable-auto-import" CACHE INTERNAL "")
   endif()
   if (MSVC)
-    set(CMAKE_CXX_FLAGS_ADD "/wd 4355 /wd 4251 /wd 4180")
+    set(CMAKE_CXX_FLAGS_ADD "/wd4355 /wd4251 /wd4180")
     list(APPEND OROCOS-RTT_LIBRARIES kernel32.lib user32.lib gdi32.lib winspool.lib shell32.lib  ole32.lib oleaut32.lib uuid.lib comdlg32.lib advapi32.lib)
     # We force to ON
     message("Forcing OS_NO_ASM to ON for MSVC.")
diff --git a/src/os/win32/fosi.cpp b/src/os/win32/fosi.cpp
index eedd052..61a80a7 100644
--- a/src/os/win32/fosi.cpp
+++ b/src/os/win32/fosi.cpp
@@ -51,12 +51,14 @@ extern "C"
 unsigned int sleep(unsigned int s)
 {
   Sleep(s*1000);
+  return 0;
 }
 
 #if __GNUC__ != 4
 int usleep(unsigned int us)
 {
     Sleep( us / 1000 );
+    return 0;
 }
 #endif