diff --git a/CMakeLists.txt b/CMakeLists.txt
index b2f137a..3754095 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -40,7 +40,7 @@ message(STATUS "VERSION = ${VERSION}, BUILD = ${BUILD}")
 
 # 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)
 if(CMAKE_SYSTEM_PROCESSOR_LC MATCHES "x86_64" OR
   CMAKE_SYSTEM_PROCESSOR_LC MATCHES "amd64" OR
   CMAKE_SYSTEM_PROCESSOR_LC MATCHES "i[0-9]86" OR
