diff --git a/CMakeLists.txt b/CMakeLists.txt
index 76a4d6fc57..a628ff98d2 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -75,7 +75,7 @@ if (NOT DEFINED INSTALL_DIR)
   endif()
   set (INSTALL_DIR "${CMAKE_INSTALL_PREFIX}" CACHE PATH "${INSTALL_DIR_DESCR}")
 else()
-  file (TO_CMAKE_PATH ${INSTALL_DIR} INSTALL_DIR)
+  file (TO_CMAKE_PATH "${INSTALL_DIR}" INSTALL_DIR)
   set (INSTALL_DIR "${INSTALL_DIR}" CACHE PATH "${INSTALL_DIR_DESCR}" FORCE)
 endif()
 
@@ -381,7 +381,7 @@ if (NOT DEFINED 3RDPARTY_DIR)
   set (3RDPARTY_DIR "" CACHE PATH ${3RDPARTY_DIR_DESCR})
   get_filename_component (3RDPARTY_DIR "${3RDPARTY_DIR}" ABSOLUTE)
 else()
-  file (TO_CMAKE_PATH ${3RDPARTY_DIR} 3RDPARTY_DIR)
+  file (TO_CMAKE_PATH "${3RDPARTY_DIR}" 3RDPARTY_DIR)
   set (3RDPARTY_DIR "${3RDPARTY_DIR}" CACHE PATH "${3RDPARTY_DIR_DESCR}" FORCE)
 endif()