diff --git a/src/config/NTMakefile.i386_nt40 b/src/config/NTMakefile.i386_nt40
index bbc002a5be..1b141ebdb0 100644
--- a/src/config/NTMakefile.i386_nt40
+++ b/src/config/NTMakefile.i386_nt40
@@ -319,6 +319,9 @@ ldebug = /NODEFAULTLIB:LIBC
 #ldebug = $(ldebug) -debugtype:cv 
 #!ENDIF
 
+# Disable optimization; generate full debug info in obj.
+afscflags = $(afscflags) /Od /Zi
+
 !IFDEF VADUMP
 ldebug = $(ldebug) -debugtype:both
 ldebug = $(ldebug:-debugtype:cv=)