diff --git a/Makefile b/Makefile
index 179c932..0d5041e 100644
--- a/Makefile
+++ b/Makefile
@@ -91,8 +91,8 @@ update_net: net.rrd
 
 disk.rrd:
 	rrdtool create $@ --start $$(( $(NOW) - 1 )) --step $(STEP) --no-overwrite \
-		DS:MBfsfree:COUNTER:120:0:U \
-		DS:MBfsused:COUNTER:120:0:U \
+		DS:mbfsfree:COUNTER:120:0:U \
+		DS:mbfsused:COUNTER:120:0:U \
 		RRA:LAST:0.5:1:1440 \
 		RRA:AVERAGE:0.5:420:1440 \
 		RRA:AVERAGE:0.5:1860:1440 \
@@ -160,10 +160,10 @@ $(BUILD_DIR)/net-daily$(EXTENSION): net.rrd
 
 $(BUILD_DIR)/disk-daily$(EXTENSION): disk.rrd
 	rrdtool graph $@ --imgformat $(FORMAT) --end now --start end-$(DAY_IN_SECS) \
-		DEF:MBfsfree=$<:MBfsfree:AVERAGE \
-		DEF:MBfsused=$<:MBfsused:AVERAGE \
-		AREA:MBfsused#$(DANGER):MBfsused:STACK \
-		AREA:MBfsfree#$(SUCCESS):MBfsfree:STACK
+		DEF:mbfsfree=$<:mbfsfree:AVERAGE \
+		DEF:mbfsused=$<:mbfsused:AVERAGE \
+		AREA:mbfsused#$(DANGER):mbfsused:STACK \
+		AREA:mbfsfree#$(SUCCESS):mbfsfree:STACK
 
 $(BUILD_DIR)/%.html: %.php
 	php $< >$@