diff --git a/ChangeLog b/ChangeLog
index 423a2d51..9e53e308 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -10,6 +10,7 @@ NEW the chi^2 calculation in single-histogram and asymmetry fits is parallelized
     if musrfit is built using a compiler supporting OpenMP (e.g. GCC >= 4.2)
     Using --disable-omp this feature can be disabled on the configure level.
 NEW any2many: force the user to define the exact NeXus ouput format (HDF4,HDF5,XML)
+FIXED crash in case a non-existing userFcn is called from an existing library (MUSR-159)
 FIXED slightly wrong chisq since the 0-bin entries were treated wrongly for scaled N0/Bkg data (MUSR-193)
 FIXED the evaluation of the LF depolarization functions (before numerous unnecessary calculations were performed)
 FIXED casting problem between uint32 and time_t for some compilers (MUSR-185)
diff --git a/src/classes/PMsrHandler.cpp b/src/classes/PMsrHandler.cpp
index d527864c..8b291f67 100644
--- a/src/classes/PMsrHandler.cpp
+++ b/src/classes/PMsrHandler.cpp
@@ -1176,7 +1176,7 @@ Int_t PMsrHandler::WriteMsrFile(const Char_t *filename, map<UInt_t, TString> *co
 
   // write FITPARAMETER block
   fout << "FITPARAMETER" << endl;
-  fout << "#       No Name        Value     Step        Pos_Error   Boundaries" << endl;
+  fout << "#      No Name        Value     Step        Pos_Error   Boundaries" << endl;
 
   for (i = 0; i < fParam.size(); ++i) {
     if (commentsPAR) {
diff --git a/src/classes/PTheory.cpp b/src/classes/PTheory.cpp
index 30703839..25441666 100644
--- a/src/classes/PTheory.cpp
+++ b/src/classes/PTheory.cpp
@@ -281,6 +281,18 @@ PTheory::PTheory(PMsrHandler *msrInfo, UInt_t runNo, const Bool_t hasParent) : f
           tokens = 0;
         }
         return;
+      } else if (!TClass::GetDict(fUserFcnClassName.Data())) {
+        cerr << endl << ">> PTheory::PTheory: **ERROR** user function class '" << fUserFcnClassName.Data() << "' not found.";
+        cerr << endl << ">>           " << fUserFcnSharedLibName.Data() << " loaded successfully, but no dictionary present.";
+        cerr << endl << ">>           See line no " << line->fLineNo;
+        cerr << endl;
+        fValid = false;
+        // clean up
+        if (tokens) {
+          delete tokens;
+          tokens = 0;
+        }
+        return;
       }
     }