diff --git a/CMakeLists.txt b/CMakeLists.txt
index 17a9483a4..b176c0eba 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -372,8 +372,6 @@ if(USE_MAGICK)
 endif()
 
 if(WANT_ZLIB AND NOT USE_ZLIB)
-	set(CMAKE_C_FLAGS_RELEASE_OLD "${CMAKE_C_FLAGS_RELEASE}")
-	set(CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS_RELEASE} -fno-lto")
 	add_subdirectory(${CMAKE_SOURCE_DIR}/src/third-party/zlib zlib)
 	set_property(TARGET zlibstatic PROPERTY INCLUDE_DIRECTORIES ${CMAKE_BINARY_DIR}/zlib;${CMAKE_SOURCE_DIR}/src/third-party/zlib)
 	set_property(TARGET zlib PROPERTY EXCLUDE_FROM_ALL ON)
@@ -382,7 +380,6 @@ if(WANT_ZLIB AND NOT USE_ZLIB)
 	set(ZLIB_INCLUDE_DIRS ${CMAKE_SOURCE_DIR}/src/third-party/zlib ${CMAKE_BINARY_DIR}/zlib)
 	set(ZLIB_INCLUDE_DIR ${CMAKE_SOURCE_DIR}/src/third-party/zlib ${CMAKE_BINARY_DIR}/zlib)
 	set(ZLIB_LIBRARY zlibstatic)
-	set(CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS_RELEASE_OLD}")
 	list(APPEND DEPENDENCY_LIB zlibstatic)
 	set(USE_ZLIB ON)
 endif()
@@ -399,12 +396,9 @@ if(WANT_PNG AND USE_ZLIB AND NOT USE_PNG)
 	set(PNG_SHARED OFF CACHE BOOL "" FORCE)
 	set(PNG_TESTS OFF CACHE BOOL "" FORCE)
 	set(SKIP_INSTALL_ALL ON)
-	set(CMAKE_C_FLAGS_RELEASE_OLD "${CMAKE_C_FLAGS_RELEASE}")
-	set(CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS_RELEASE} -fno-lto")
 	add_subdirectory(${CMAKE_SOURCE_DIR}/src/third-party/libpng libpng)
 	set_property(TARGET png16_static PROPERTY INCLUDE_DIRECTORIES ${CMAKE_BINARY_DIR}/libpng;${CMAKE_SOURCE_DIR}/src/third-party/libpng;${ZLIB_INCLUDE_DIRS})
 	set(PNG_INCLUDE_DIRS ${CMAKE_SOURCE_DIR}/src/third-party/libpng ${CMAKE_BINARY_DIR}/libpng)
-	set(CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS_RELEASE_OLD}")
 	list(APPEND DEPENDENCY_LIB png16_static)
 	set(USE_PNG ON)
 endif()