diff --git a/CMakeLists.txt b/CMakeLists.txt
index 17ee3fc..c01ec57 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -186,7 +186,7 @@
 target_compile_definitions(opus PRIVATE OPUS_BUILD ENABLE_HARDENING)
 
 if(NOT MSVC)
-  target_compile_definitions(opus PRIVATE FORTIFY_SOURCE=2)
+  target_compile_definitions(opus PRIVATE _FORTIFY_SOURCE=2)
 endif()
 
 # It is strongly recommended to uncomment one of these VAR_ARRAYS: Use C99