diff --git a/CMakeLists.txt b/CMakeLists.txt
index d3fbad30..9cf01cf5 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -89,7 +89,7 @@ include(cmakescripts/PackageInfo.cmake)
 
 # Detect CPU type and whether we're building 64-bit or 32-bit code
 math(EXPR BITS "${CMAKE_SIZEOF_VOID_P} * 8")
-string(TOLOWER ${CMAKE_SYSTEM_PROCESSOR} CMAKE_SYSTEM_PROCESSOR_LC)
+string(TOLOWER "${CMAKE_SYSTEM_PROCESSOR}" CMAKE_SYSTEM_PROCESSOR_LC)
 set(COUNT 1)
 foreach(ARCH ${CMAKE_OSX_ARCHITECTURES})
   if(COUNT GREATER 1)