diff --git a/Makefile.PL b/Makefile.PL
index ef29a950c..f1df8bcd3 100755
--- a/Makefile.PL
+++ b/Makefile.PL
@@ -96,7 +96,7 @@ underlay_install:
 		install -d $(DESTDIR)$(PREFIX)/share/ikiwiki/$$theme; \
 		for file in $$theme/*; do \
 			if echo "$$file" | grep -q style.css; then \
-				(cat doc/style.css; cat $$theme/base.css 2>/dev/null; cat $$file) >> $(DESTDIR)$(PREFIX)/share/ikiwiki/$$theme/style.css; \
+				(cat doc/style.css; cat $$theme/base.css 2>/dev/null; cat $$file) > $(DESTDIR)$(PREFIX)/share/ikiwiki/$$theme/style.css; \
 			elif echo "$$file" | grep -q base.css; then \
 				:; \
 			elif [ -f "$$file" ]; then \