diff --git a/Modules/FindRTI.cmake b/Modules/FindRTI.cmake
index be3ad8f137..434f4a7f59 100644
--- a/Modules/FindRTI.cmake
+++ b/Modules/FindRTI.cmake
@@ -38,7 +38,7 @@ SET(RTI_POSSIBLE_DIRS
   "[HKEY_LOCAL_MACHINE\\SOFTWARE\\MAK Technologies\\MAK RTI 2.2;Location]"
   "[HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Uninstall\\MAK RTI 2.2;InstallLocation]")
 
-SET(RTI_OLD_FIND_LIBRARY_PREFIXES ${CMAKE_FIND_LIBRARY_PREFIXES})
+SET(RTI_OLD_FIND_LIBRARY_PREFIXES "${CMAKE_FIND_LIBRARY_PREFIXES}")
 # The MAK RTI has the "lib" prefix even on Windows.
 SET(CMAKE_FIND_LIBRARY_PREFIXES "lib" "")
 
@@ -79,7 +79,7 @@ ELSE (RTI_INCLUDE_DIR)
 ENDIF (RTI_INCLUDE_DIR)
 
 # Set the modified system variables back to the original value.
-SET(CMAKE_FIND_LIBRARY_PREFIXES ${RTI_OLD_FIND_LIBRARY_PREFIXES})
+SET(CMAKE_FIND_LIBRARY_PREFIXES "${RTI_OLD_FIND_LIBRARY_PREFIXES}")
 
 INCLUDE(FindPackageHandleStandardArgs)
 FIND_PACKAGE_HANDLE_STANDARD_ARGS(RTI DEFAULT_MSG