diff --git a/CMakeLists.txt b/CMakeLists.txt
index e076d5e..428cf68 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -78,8 +78,8 @@ set(PNG_PREFIX "" CACHE STRING "Prefix to add to the API function names")
 set(DFA_XTRA "" CACHE FILEPATH "File containing extra configuration settings")
 
 # set definitions and sources for arm
-if(${CMAKE_SYSTEM_PROCESSOR} MATCHES "^arm" OR
-  ${CMAKE_SYSTEM_PROCESSOR} MATCHES "^aarch64")
+if(CMAKE_SYSTEM_PROCESSOR MATCHES "^arm" OR
+  CMAKE_SYSTEM_PROCESSOR MATCHES "^aarch64")
   set(PNG_ARM_NEON_POSSIBLE_VALUES check on off)
   set(PNG_ARM_NEON "check" CACHE STRING "Enable ARM NEON optimizations:
      check: (default) use internal checking code;