diff --git a/common.mk b/common.mk
index b6460d4a3f..ad4e9dbad3 100644
--- a/common.mk
+++ b/common.mk
@@ -1098,7 +1098,7 @@ update-unicode: PHONY
 lib/unicode_normalize/tables.rb: tool/unicode_norm_gen.rb \
 enc/unicode/data/UnicodeData.txt \
 enc/unicode/data/CompositionExclusions.txt
-	${BASERUBY} -C "$(srcdir)/tool tool/unicode_norm_gen.rb
+	$(BASERUBY) -C "$(srcdir)/tool tool/unicode_norm_gen.rb
 
 info: info-program info-libruby_a info-libruby_so info-arch
 info-program: PHONY