Index: munin-1.4.6-1ubuntu1/plugins/node.d.linux/sensors_.in
===================================================================
--- munin-1.4.6-1ubuntu1.orig/plugins/node.d.linux/sensors_.in	2011-09-03 18:36:02.173366982 +0200
+++ munin-1.4.6-1ubuntu1/plugins/node.d.linux/sensors_.in	2011-09-03 18:47:08.997367354 +0200
@@ -104,11 +104,13 @@
                        # RPM values. Verified in lm-sensors-3-3.1.2
             (\d+)      # Match one or more digits (Match current value as \$2)
             \s         # Exactly one space followed by 
-            RPM.*?     # RPM string, and then any chars
-            (\d+)      # Match one or more digits (Match minimum value as \$3)
-            \s         # Exactly one space followed by
+            (?:        # a optional group, which might contain the minimum value:
+              RPM.*?   # RPM string, and then any chars (but no newlines)
+              (\d+)    # Match one or more digits (Match minimum value as \$3)
+              \s       # Exactly one space followed by
+            )?         # end of optional group
             RPM        # RPM string
-                /xms,
+                /xm,
             title => 'Fans',
             vtitle => 'RPM',
             print_threshold => \&fan_threshold,