--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -38,7 +38,7 @@
 include (FindPerlMore)
 string(LENGTH "${PERL_INSTALL_PREFIX}" PERL_INSTALL_PREFIX_LEN)
 math(EXPR PERL_INSTALL_PREFIX_LEN "${PERL_INSTALL_PREFIX_LEN}+1")
-string(SUBSTRING ${PERL_SITE_ARCH_DIR} ${PERL_INSTALL_PREFIX_LEN} -1 CUSTOM_PERL_SITE_ARCH_DIR)
+string(SUBSTRING ${PERL_VENDOR_ARCH_DIR} ${PERL_INSTALL_PREFIX_LEN} -1 CUSTOM_PERL_SITE_ARCH_DIR)
 file(TO_NATIVE_PATH "${CMAKE_INSTALL_PREFIX}/${CUSTOM_PERL_SITE_ARCH_DIR}" CUSTOM_PERL_SITE_ARCH_DIR)
 set(CUSTOM_PERL_SITE_ARCH_DIR ${CUSTOM_PERL_SITE_ARCH_DIR} CACHE DIR "Custom installation directory for perl binary extension")