diff --git a/orocos-rtt-config.cmake b/orocos-rtt-config.cmake
index 5a8d9d8e4..84e974b96 100644
--- a/orocos-rtt-config.cmake
+++ b/orocos-rtt-config.cmake
@@ -65,12 +65,12 @@
 ########################################################################################################################
 
 # Set the default target operating system, if unspecified
-if(NOT DEFINED OROCOS_TARGET)
-  set(DOC_STRING "The Operating System target. One of [gnulinux lxrt macosx win32 xenomai]")
-  if(NOT $ENV{OROCOS_TARGET} STREQUAL "")
-    set(OROCOS_TARGET $ENV{OROCOS_TARGET} CACHE STRING "${DOC_STRING}")
-    message( "Detected OROCOS_TARGET environment variable. Using: ${OROCOS_TARGET}")
-  else()
+set(DOC_STRING "The Operating System target. One of [gnulinux lxrt macosx win32 xenomai]")
+if(NOT $ENV{OROCOS_TARGET} STREQUAL "")
+  set(OROCOS_TARGET $ENV{OROCOS_TARGET} CACHE STRING "${DOC_STRING}" FORCE)
+  message( "Detected OROCOS_TARGET environment variable. Using: ${OROCOS_TARGET}")
+else()
+  if(NOT DEFINED OROCOS_TARGET)
     if(MSVC)
       set(OROCOS_TARGET win32    CACHE STRING "${DOC_STRING}")
     elseif(APPLE AND ${CMAKE_SYSTEM_NAME} MATCHES "Darwin")