diff --git a/src/Makefile b/src/Makefile
index b8cf780..a5b9838 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -34,11 +34,11 @@ base64u.o client.o iodined.o: base64u.h
 base64u.c: base64.c
 	@echo Making $@
 	@echo '/* No use in editing, produced by Makefile! */' > $@
-	@sed -e 's/\(base64\)/\1u/ig ; s/0123456789+/0123456789_/' < $< >> $@
+	@sed -e 's/\([Bb][Aa][Ss][Ee]64\)/\1u/g ; s/0123456789+/0123456789_/' < base64.c >> $@
 base64u.h: base64.h
 	@echo Making $@
 	@echo '/* No use in editing, produced by Makefile! */' > $@
-	@sed -e 's/\(base64\)/\1u/ig ; s/0123456789+/0123456789_/' < $< >> $@
+	@sed -e 's/\([Bb][Aa][Ss][Ee]64\)/\1u/g ; s/0123456789+/0123456789_/' < base64.h >> $@
 
 clean:
 	@echo "Cleaning src/"