diff --git a/CMakeLists.txt b/CMakeLists.txt
index a02a73f..ad64710 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -5,8 +5,8 @@ project(tzdb2nx VERSION 1.0)
 option(TZDB2NX_ZONEINFO_DIR "Specify a custom zoneinfo directory containing time zone data you wish to use" "")
 option(TZDB2NX_VERSION "Specify a custom zoneinfo version with the directory" "")
 
-if ((TZDB2NX_ZONEINFO_DIR AND NOT TZDB2NX_VERSION) OR (TZDB2NX_VERSION AND NOT TZDB2NX_ZONEINFO_DIR))
-    message(FATAL_ERROR "Either TZDB2NX_ZONEINFO_DIR or TZDB2NX_VERSION but not both were defined.")
+if (TZDB2NX_ZONEINFO_DIR AND NOT TZDB2NX_VERSION)
+    message(FATAL_ERROR "TZDB2NX_ZONEINFO_DIR was specified but TZDB2NX_VERSION was left undefined.")
 endif()
 
 set(CMAKE_CXX_STANDARD 20)