diff --git a/dtool/Config.pp b/dtool/Config.pp
index ca56eb3e48..f8424fff04 100644
--- a/dtool/Config.pp
+++ b/dtool/Config.pp
@@ -532,10 +532,10 @@
 // options to interrogate, guaranteeing that the correct interfaces
 // are generated.  Do not include -D here; that will be supplied
 // automatically.
-#defer CDEFINES_OPT1 _DEBUG
-#defer CDEFINES_OPT2 _DEBUG
-#defer CDEFINES_OPT3
-#defer CDEFINES_OPT4 NDEBUG
+#defer CDEFINES_OPT1 _DEBUG $[EXTRA_CDEFS]
+#defer CDEFINES_OPT2 _DEBUG $[EXTRA_CDEFS]
+#defer CDEFINES_OPT3 $[EXTRA_CDEFS]
+#defer CDEFINES_OPT4 NDEBUG $[EXTRA_CDEFS]
 
 // What additional flags should be passed for each value of OPTIMIZE
 // (above)?  We separate out the compiler-optimization flags, above,