diff --git a/CMakeLists.txt b/CMakeLists.txt
index 27d9f09bd..64b8ac75c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -261,10 +261,6 @@ if(DEFINED 3DS OR DEFINED PSP2 OR DEFINED WII OR DEFINED SWITCH)
 	set(USE_LIBZIP OFF CACHE BOOL "")
 endif()
 
-if(DEFINED 3DS)
-	add_definitions(-DFIXED_ROM_BUFFER)
-endif()
-
 if(DEFINED SWITCH)
 	set(BUILD_GLES3 ON CACHE BOOL "Build with OpenGL|ES 3" FORCE)
 endif()
@@ -282,10 +278,6 @@ if(WII)
 	add_definitions(-U__STRICT_ANSI__)
 endif()
 
-if(3DS OR WII)
-	add_definitions(-D_GNU_SOURCE)
-endif()
-
 include(CheckCCompilerFlag)
 include(CheckFunctionExists)
 include(CheckIncludeFiles)
diff --git a/src/platform/3ds/CMakeLists.txt b/src/platform/3ds/CMakeLists.txt
index b077ca53a..29da450fa 100644
--- a/src/platform/3ds/CMakeLists.txt
+++ b/src/platform/3ds/CMakeLists.txt
@@ -10,7 +10,7 @@ find_program(RAW2C raw2c)
 set(STRIP "${cross_prefix_path}strip" CACHE INTERNAL "symbol stripper")
 
 set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wno-format" PARENT_SCOPE)
-set(OS_DEFINES COLOR_16_BIT COLOR_5_6_5 IOAPI_NO_64)
+set(OS_DEFINES _GNU_SOURCE COLOR_16_BIT COLOR_5_6_5 FIXED_ROM_BUFFER IOAPI_NO_64)
 
 include_directories(${CMAKE_CURRENT_BINARY_DIR})
 if(${CMAKE_BUILD_TYPE} STREQUAL Debug OR ${CMAKE_BUILD_TYPE} STREQUAL RelWithDebInfo)
diff --git a/src/platform/wii/CMakeLists.txt b/src/platform/wii/CMakeLists.txt
index d0a1a7821..318c176a6 100644
--- a/src/platform/wii/CMakeLists.txt
+++ b/src/platform/wii/CMakeLists.txt
@@ -3,7 +3,7 @@ find_program(GXTEXCONV gxtexconv)
 find_program(RAW2C raw2c)
 find_program(WIILOAD wiiload)
 
-set(OS_DEFINES COLOR_16_BIT COLOR_5_6_5 USE_VFS_FILE IOAPI_NO_64 FIXED_ROM_BUFFER)
+set(OS_DEFINES _GNU_SOURCE COLOR_16_BIT COLOR_5_6_5 USE_VFS_FILE IOAPI_NO_64 FIXED_ROM_BUFFER)
 list(APPEND CORE_VFS_SRC ${CMAKE_SOURCE_DIR}/src/util/vfs/vfs-file.c ${CMAKE_SOURCE_DIR}/src/util/vfs/vfs-dirent.c ${CMAKE_SOURCE_DIR}/src/util/vfs/vfs-devlist.c)
 
 include_directories(${CMAKE_CURRENT_BINARY_DIR})