diff --git a/mozilla/build/mac/BuildNGLayoutDebug.pl b/mozilla/build/mac/BuildNGLayoutDebug.pl
index 3eaa456e078..b4d7ed0a736 100644
--- a/mozilla/build/mac/BuildNGLayoutDebug.pl
+++ b/mozilla/build/mac/BuildNGLayoutDebug.pl
@@ -63,11 +63,11 @@ $build{xpapp} 			= 0;
 # the outcome.
 #-----------------------------------------------
 $ALIAS_SYM_FILES		= $DEBUG;
-$CLOBBER_LIBS			= 1;	# turn on to clobber existing libs and .xSYM files before
+$CLOBBER_LIBS			= 0;	# turn on to clobber existing libs and .xSYM files before
 								# building each project							
 # The following two options will delete all dist files (if you have $build{dist} turned on),
 # but leave the directory structure intact.
-$CLOBBER_DIST_ALL 		= 1;	# turn on to clobber all aliases/files inside dist (headers/xsym/libs)
+$CLOBBER_DIST_ALL 		= 0;	# turn on to clobber all aliases/files inside dist (headers/xsym/libs)
 $CLOBBER_DIST_LIBS 		= 0;	# turn on to clobber only aliases/files for libraries/sym files in dist
 
 #-----------------------------------------------