diff --git a/CMakeLists.txt b/CMakeLists.txt
index af3defbff63..2274f6ed630 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -322,7 +322,11 @@ if(CMAKE_SYSTEM_NAME MATCHES "Linux")
             SET(FLTO_COMPILE_OPTS "-fno-lto")
             SET(FLTO_LINK_OPTS "-fno-lto")
         else()
-            SET(FLTO_COMPILE_OPTS "-flto" "-${USING_LTO}")
+            if (DEFINED USING_LTO)
+                SET(FLTO_COMPILE_OPTS "-flto" "-${USING_LTO}")
+            else()
+                SET(FLTO_COMPILE_OPTS "-flto")
+            endif()
             SET(FLTO_LINK_OPTS "-flto")
         endif()
         SET(CMAKE_SHARED_LIBRARY_LINK_C_FLAGS "")