diff --git a/CMakeLists.txt b/CMakeLists.txt
index 58ae27d23..bbc129eae 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -264,8 +264,8 @@ if(APPLE)
         set(NOTARY "${NOTARY}" CACHE STRING "Notarization Identity")
     endif()
     if("${LOCAL_PREFIX}")
-        set(LOCAL_PREFIX "${LOCAL_PREFIX}" CACHE STRING "macos/gtk parent directory, ie. /usr or /opt")
-    else()
+        set(LOCAL_PREFIX "${LOCAL_PREFIX}" CACHE STRING "macos/gtk parent directory ie /usr or /opt")
+    elseif(NOT DEFINED LOCAL_PREFIX)
         set(LOCAL_PREFIX "/usr")
     endif()
 endif()