diff --git a/CMakeLists.txt b/CMakeLists.txt
index 98dcc9f2..57c6539b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -14,21 +14,21 @@ option(BMWlibs "build optional BMWlibs" OFF)
 option(BNMRlibs "build optional beta-NMR libs" OFF)
 option(qt_based_tools "try to install Qt based tools (musredit, musrWiz, musrStep, mupp)" ON)
 option(try_OpenMP "try to use OpenMP if available" ON)
-# define qt_version with possible values 'auto' or version '3', '4', '5'
+# define qt_version with possible values 'auto' or version '3', '4', '5', '6'
 set(qt_version AUTO CACHE STRING "provide a specific Qt version to be used.")
-set_property(CACHE qt_version PROPERTY STRINGS AUTO 3 4 5)
+set_property(CACHE qt_version PROPERTY STRINGS AUTO 3 4 5 6)
 
 #--- set a default build type if none was specified ---------------------------
 set(default_build_type "Release")
- 
-if(NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
+  
+if (NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
   message(STATUS "Setting build type to '${default_build_type}' as none was specified.")
   set(CMAKE_BUILD_TYPE "${default_build_type}" CACHE
       STRING "Choose the type of build." FORCE)
   # Set the possible values of build type for cmake-gui
   set_property(CACHE CMAKE_BUILD_TYPE PROPERTY STRINGS
     "Debug" "Release" "MinSizeRel" "RelWithDebInfo")
-endif()
+endif ()
 
 #--- perform some checks and generate the config.h ----------------------------
 
diff --git a/src/classes/PMsrHandler.cpp b/src/classes/PMsrHandler.cpp
index 84408668..b40ae3db 100644
--- a/src/classes/PMsrHandler.cpp
+++ b/src/classes/PMsrHandler.cpp
@@ -6674,10 +6674,12 @@ void PMsrHandler::MakeDetectorGroupingString(TString str, PIntVector &group, TSt
   UInt_t i=0, j=0;
   do {
     j = i;
-    while (group[j]+1 == group[j+1]) {
-      j++;
-      if (j == group.size()-1)
-        break;
+    if (j+1 < group.size()) {
+      while (group[j]+1 == group[j+1]) {
+        j++;
+        if (j == group.size()-1)
+          break;
+      }
     }
 
     if (j >= i+2) {