diff --git a/mozilla/config/Makefile b/mozilla/config/Makefile
index 8eb36e235f4..2a28e4f16f2 100644
--- a/mozilla/config/Makefile
+++ b/mozilla/config/Makefile
@@ -32,7 +32,9 @@ PLSRCS		= nfspwd.pl revdepth.pl
 TARGETS		= $(PROGRAM) $(PLSRCS:.pl=)
 
 # Generate the build number on the fly.
+ifdef BUILD_OFFICIAL
 TARGETS		+= $(DEPTH)/build/build_number
+endif
 
 ifneq ($(subst /,_,$(shell uname -s)),WINNT)
 PROGRAM		= nsinstall$(BIN_SUFFIX)