diff --git a/3rdparty/libjpeg-turbo/CMakeLists.txt b/3rdparty/libjpeg-turbo/CMakeLists.txt
index ac0aaf63e1..6e508c8860 100644
--- a/3rdparty/libjpeg-turbo/CMakeLists.txt
+++ b/3rdparty/libjpeg-turbo/CMakeLists.txt
@@ -16,7 +16,7 @@ endif()
 message(STATUS "libjpeg-turbo: VERSION = ${VERSION}, BUILD = ${BUILD}")
 
 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