diff --git a/CMakeLists.txt b/CMakeLists.txt
index 3eb6a1927..abb188577 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -277,9 +277,7 @@ endif()
 # check for change in arch (32<->64)
 if(UNIX)
     GET_PROPERTY(DFHACK_CACHED_ARCH CACHE STRING PROPERTY DFHACK_BUILD_ARCH)
-    if("${DFHACK_BUILD_ARCH}" STREQUAL "${DFHACK_CACHED_ARCH}")
-        # no change
-    else()
+	if(NOT "${DFHACK_BUILD_ARCH}" STREQUAL "${DFHACK_CACHED_ARCH}")
         unset(ZLIB_LIBRARY CACHE)
         unset(CMAKE_HAVE_PTHREAD_H CACHE)
     endif()