diff --git a/CMakeLists.txt b/CMakeLists.txt
index 20d653a082..9f41f03241 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -86,10 +86,16 @@ main(void)
 " _FORTIFY_SOURCE_ACCEPTABLE)
 
 if(NOT _FORTIFY_SOURCE_ACCEPTABLE)
+  # Extract possible prefix to _FORTIFY_SOURCE (e.g. -Wp,-D_FORTIFY_SOURCE).
+  STRING(REGEX MATCH "[^\ ]+-D_FORTIFY_SOURCE" _FORTIFY_SOURCE_PREFIX "${CMAKE_C_FLAGS}")
+  STRING(REPLACE "-D_FORTIFY_SOURCE" "" _FORTIFY_SOURCE_PREFIX "${_FORTIFY_SOURCE_PREFIX}" )
+  if (NOT _FORTIFY_SOURCE_PREFIX STREQUAL "")
+    message(STATUS "Detected _FORTIFY_SOURCE Prefix=${_FORTIFY_SOURCE_PREFIX}")
+  endif()
   # -U in add_definitions doesn't end up in the correct spot, so we add it to
   # the flags variable instead.
-  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=1")
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=1")
+  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${_FORTIFY_SOURCE_PREFIX}-U_FORTIFY_SOURCE ${_FORTIFY_SOURCE_PREFIX}-D_FORTIFY_SOURCE=1")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${_FORTIFY_SOURCE_PREFIX}-U_FORTIFY_SOURCE ${_FORTIFY_SOURCE_PREFIX}-D_FORTIFY_SOURCE=1")
 endif()
 
 add_definitions(-Wall -Wextra -pedantic -Wno-unused-parameter