diff --git a/MDStatMonitoringUnit.cs b/MDStatMonitoringUnit.cs
index abfba99..4d55811 100644
--- a/MDStatMonitoringUnit.cs
+++ b/MDStatMonitoringUnit.cs
@@ -38,6 +38,12 @@ namespace Barsik
 					// 2930264896 blocks super 1.0 [2/2] [UU]
 					// we need last characters in brackets []
 					int last_pos = lines[i + 1].LastIndexOf(']');
+					if (last_pos == -1)
+					{
+						// This can happen for inactive RAID devices. Skip this device for now
+						i += 2;
+						continue;
+					}
 					int pos;
 					for (pos = last_pos; pos > 0 && lines[i + 1][pos] != '['; pos--) ;
 					if (lines[i + 1][pos] != '[') knownRaids.Add(0);
@@ -94,7 +100,8 @@ namespace Barsik
 				var lines = File.ReadAllLines("/proc/mdstat");
 				for (int i = 0; i < lines.Length;)
 				{
-					if (lines[i].StartsWith("md") && i < lines.Length - 1)
+					if (lines[i].StartsWith("md") && i < lines.Length - 1 &&
+						lines[i + 1].LastIndexOf(']') != -1)
 					{
 						// we found device description
 						// second line of it is as follows: