diff --git a/CMakeLists.txt b/CMakeLists.txt
index 31464b5de..57974a9f9 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -468,15 +468,13 @@ SET(CMAKE_DEBUG_POSTFIX "d" CACHE STRING "add a postfix, usually d on windows")
 ADD_DEFINITIONS(-DOSG_DEBUG_POSTFIX=${CMAKE_DEBUG_POSTFIX})
 
 IF(UNIX AND NOT WIN32)
-  IF(CMAKE_BUILD_TYPE STREQUAL "Debug")
-    ADD_DEFINITIONS("-D_DEBUG")
-  ENDIF()
+  SET(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} -D_DEBUG")
+  SET(CMAKE_C_FLAGS_DEBUG "${CMAKE_C_FLAGS_DEBUG} -D_DEBUG")
 ENDIF()
 
 IF(CYGWIN)
-  IF(CMAKE_BUILD_TYPE STREQUAL "Debug")
-    ADD_DEFINITIONS("-D_DEBUG")
-  ENDIF()
+  SET(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} -D_DEBUG")
+  SET(CMAKE_C_FLAGS_DEBUG "${CMAKE_C_FLAGS_DEBUG} -D_DEBUG")
 ENDIF()
 
 IF(UNIX AND NOT WIN32 AND NOT APPLE)