diff --git a/ExternalLibs/FTGL.cmake b/ExternalLibs/FTGL.cmake
index 71aca5d..e6bf617 100644
--- a/ExternalLibs/FTGL.cmake
+++ b/ExternalLibs/FTGL.cmake
@@ -4,8 +4,8 @@ if(AQUARIA_INTERNAL_FTGL)
     SET(FTGLDIR ${CMAKE_CURRENT_SOURCE_DIR}/FTGL)
     set(FTGL_INCLUDE_DIRS "${FTGLDIR}/include;${FREETYPE_INCLUDE_DIRS}" CACHE INTERNAL "")
     include(freetype2.cmake) # Nothing else uses freetype2 directly
-    INCLUDE_DIRECTORIES(${FREETYPE_INCLUDE_DIRS})
-    INCLUDE_DIRECTORIES(${EXTLIBDIR}) # For <GL/gl.h>
+    INCLUDE_DIRECTORIES("${FREETYPE_INCLUDE_DIRS}")
+    INCLUDE_DIRECTORIES("${EXTLIBDIR}") # For <GL/gl.h>
     add_subdirectory(FTGL)
 else()
     find_package(FTGL REQUIRED)