diff --git a/CMakeLists.txt b/CMakeLists.txt
index 821f170..5b0b070 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -112,9 +112,9 @@ if(NOT HH_PESIEVE_LINK_MODE STREQUAL "STATIC"
 endif()
 
 if(HH_PESIEVE_LINK_MODE STREQUAL "STATIC")
-	set(PESIEVE_BUILD_MODE "STATIC" CACHE STRING "Build mode for PE-sieve" FORCE)
+	set(PESIEVE_BUILD_MODE "STATIC" CACHE INTERNAL "Build mode for PE-sieve" FORCE)
 elseif(HH_PESIEVE_LINK_MODE STREQUAL "DLL")
-	set(PESIEVE_BUILD_MODE "DLL" CACHE STRING "Build mode for PE-sieve" FORCE)
+	set(PESIEVE_BUILD_MODE "DLL" CACHE INTERNAL "Build mode for PE-sieve" FORCE)
 endif()
 
 add_subdirectory ( ${PESIEVE_DIR} )