diff --git a/CMakeLists.txt b/CMakeLists.txt
index 292f1f4fc..325bf6d39 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -89,6 +89,25 @@ ja2_asan_instrument_first_party()
 # from here on down our own code only: vendored code above keeps default flags
 include(cmake/Warnings.cmake)
 
+# Compile-time switches for our own code. These belong to the build system, not
+# to a header: a #define buried in the source tree is invisible to anyone reading
+# the build files, and cannot be varied per configuration. Nothing below should
+# ever be reintroduced as a bare #define.
+add_compile_definitions(
+  # 0verhaul: squelch the VC2K5+ warnings about printf and string operations
+  # being unsafe, so real errors stay visible.
+  _CRT_SECURE_NO_WARNINGS
+  _CRT_NON_CONFORMING_SWPRINTFS
+  _SCL_SECURE_NO_WARNINGS
+
+  # Laptop briefing room (Jazz). Also needs BRIEFING_ROOM in ja2_options.ini and
+  # a briefing-room mod, otherwise the room comes up blank.
+  ENABLE_BRIEFINGROOM
+  ROBOT_ALWAYS_READY
+  # keep Assert() live in configurations that would otherwise compile it out
+  FORCE_ASSERTS_ON
+)
+
 # ja2export utility
 add_subdirectory("export/src")
 
diff --git a/Ja2/builddefines.h b/Ja2/builddefines.h
index 07e1489de..9a7b11933 100644
--- a/Ja2/builddefines.h
+++ b/Ja2/builddefines.h
@@ -1,84 +1,10 @@
-#ifndef _BUILDDEFINES_H
-#define _BUILDDEFINES_H
-
-//----- Briefing Room (Mission based JA2 like in JA/DG) - by Jazz -----
-// Once enabled here and also enabled in the ja2_options.ini (BRIEFING_ROOM), 
-// you can access the briefing room feature from the laptop
-// Of course, you also need a briefing room 1.13-MOD, otherwise you have a blank briefing room.
-// There are 2 examples (Briefing Room Example 1.zip, Briefing Room Example 2.zip) in the documents svn folder:
-// https://ja2svn.dyndns.org/source/ja2/trunk/Documents/1.13%20Modding/Modding%20Examples
-#define ENABLE_BRIEFINGROOM
-
-// -----------------------------
-// *****************************
-// WANNE: Enable those 2 defines, if you want to build UB-Version!!
-
-//JA2/Unfinished Business
-//#define JA2UB
-
-//Unfinished Business - Titles (ja2set.dat)
-//#define JA2UBMAPS
-// *****************************
-// -----------------------------
-
-// -----------------------------
-// *****************************
-// WANNE: With this defin we can build JA2 DEMO version that runs with 1.13
-// The 2 UB defines (JA2UB  and JA2UBMAPS) should be disabled, because we only want to build the demo version from the JA2 code!
-
-//#define JA113DEMO
-// *****************************
-// -----------------------------
-
-// Map Editor version - you should use the MapEditor configuration instead of messing with these defines (ChrisL)
-//#ifndef JA2BETAVERSION
-//#define JA2BETAVERSION
-//#endif
-//#define JA2EDITOR
-// Normal test version
-//#define JA2TESTVERSION
-
-//#define SGP_DEBUG
-//#define DEBUG_ATTACKBUSY
-//#define DEBUGDECISIONS
-#define ROBOT_ALWAYS_READY
-#define	FORCE_ASSERTS_ON
-
-//#ifdef _DEBUG
-//	#ifndef JA2TESTVERSION
-//		#define JA2TESTVERSION
-//	#endif
-//#endif
-
-// Do combinations
-//#ifdef JA2TESTVERSION
-//	#define JA2BETAVERSION
-//	#define JA2EDITOR
-//#endif
-
-
-
-#ifdef JA2BETAVERSION
-	#ifndef JA2EDITOR
-//		#define SGP_DEBUG
-//		#define	FORCE_ASSERTS_ON
-//		#define SGP_VIDEO_DEBUGGING
-	#endif
-#endif
-
-//#define CRIPPLED_VERSION
-
-// Huge speed and memory hog, but thorough -- will work with release builds.
-// #define EXTREME_MEMORY_DEBUGGING 
-
-// 0verhaul
-// These squelch warnings in VC2K5 about printf's and string operations being unsafe.  Maybe we should work on building a better
-// system that gives buffer sizes for copies (which would prevent future problems like a stack corruption issue I fixed a while back),
-// but for now, just tell the compiler to shut up so I can see the real errors.
-#define _CRT_SECURE_NO_WARNINGS
-#define _CRT_NON_CONFORMING_SWPRINTFS
-#define _SCL_SECURE_NO_WARNINGS
-
-#include "profiler.h"
-
-#endif
+#ifndef _BUILDDEFINES_H
+#define _BUILDDEFINES_H
+
+// The compile-time switches that used to live here now live in CMakeLists.txt,
+// which is where the build system can see them. This header is empty and about
+// to be deleted; do not add anything to it.
+
+#include "profiler.h"
+
+#endif