diff --git a/examples/mdp/csma/csma3_4.nm b/examples/mdp/csma/csma3_4.nm
index c1b97fc3f..8739053e5 100644
--- a/examples/mdp/csma/csma3_4.nm
+++ b/examples/mdp/csma/csma3_4.nm
@@ -129,4 +129,6 @@ endrewards
 label "all_delivered" = s1=4&s2=4&s3=4;
 label "one_delivered" = s1=4|s2=4|s3=4;
 label "collision_max_backoff" = (cd1=K & s1=1 & b=2)|(cd2=K & s2=1 & b=2)|(cd3=K & s3=1 & b=2);
-
+formula min_backoff_after_success = min(s1=4?cd1:K+1,s2=4?cd2:K+1,s3=4?cd3:K+1);
+formula min_collisions = min(cd1,cd2,cd3);
+formula max_collisions = max(cd1,cd2,cd3);
diff --git a/examples/mdp/csma/csma4_4.nm b/examples/mdp/csma/csma4_4.nm
index 90f182dde..e1ba511f4 100644
--- a/examples/mdp/csma/csma4_4.nm
+++ b/examples/mdp/csma/csma4_4.nm
@@ -134,4 +134,6 @@ endrewards
 label "all_delivered" = s1=4&s2=4&s3=4&s4=4;
 label "one_delivered" = s1=4|s2=4|s3=4|s4=4;
 label "collision_max_backoff" = (cd1=K & s1=1 & b=2)|(cd2=K & s2=1 & b=2)|(cd3=K & s3=1 & b=2)|(cd4=K & s4=1 & b=2);
-
+formula min_backoff_after_success = min(s1=4?cd1:K+1,s2=4?cd2:K+1,s3=4?cd3:K+1,s4=4?cd4:K+1);
+formula min_collisions = min(cd1,cd2,cd3,cd4);
+formula max_collisions = max(cd1,cd2,cd3,cd4);
diff --git a/examples/mdp/csma/csma4_6.nm b/examples/mdp/csma/csma4_6.nm
index 8e9fb110a..12e5f0152 100644
--- a/examples/mdp/csma/csma4_6.nm
+++ b/examples/mdp/csma/csma4_6.nm
@@ -136,4 +136,6 @@ endrewards
 label "all_delivered" = s1=4&s2=4&s3=4&s4=4;
 label "one_delivered" = s1=4|s2=4|s3=4|s4=4;
 label "collision_max_backoff" = (cd1=K & s1=1 & b=2)|(cd2=K & s2=1 & b=2)|(cd3=K & s3=1 & b=2)|(cd4=K & s4=1 & b=2);
-
+formula min_backoff_after_success = min(s1=4?cd1:K+1,s2=4?cd2:K+1,s3=4?cd3:K+1,s4=4?cd4:K+1);
+formula min_collisions = min(cd1,cd2,cd3,cd4);
+formula max_collisions = max(cd1,cd2,cd3,cd4);
diff --git a/src/parser/ExpressionParser.cpp b/src/parser/ExpressionParser.cpp
index f6ff87f5b..7054e26ef 100644
--- a/src/parser/ExpressionParser.cpp
+++ b/src/parser/ExpressionParser.cpp
@@ -337,12 +337,8 @@ namespace storm {
                 STORM_LOG_THROW(this->identifiers_ != nullptr, storm::exceptions::WrongFormatException, "Unable to substitute identifier expressions without given mapping.");
                 storm::expressions::Expression const* expression = this->identifiers_->find(identifier);
                 if (expression == nullptr) {
-                    if (allowBacktracking) {
-                        pass = false;
-                        return manager->boolean(false);
-                    } else {
-                        pass = false;
-                    }
+                    pass = false;
+                    return manager->boolean(false);
                 }
                 return *expression;
             } else {
diff --git a/src/parser/SpiritErrorHandler.h b/src/parser/SpiritErrorHandler.h
index 3e78935bd..cd2a35b06 100644
--- a/src/parser/SpiritErrorHandler.h
+++ b/src/parser/SpiritErrorHandler.h
@@ -22,7 +22,7 @@ namespace storm {
                 stream << "Parsing error at " << get_line(where) << ":" << boost::spirit::get_column(lineStart, where) << ": " << " expecting " << what << ", here:" << std::endl;
                 stream << "\t" << line << std::endl << "\t";
                 auto caretColumn = boost::spirit::get_column(lineStart, where);
-                stream << std::string(caretColumn - 1, ' ') << "^" << std::endl;
+                stream << "\t" << std::string(caretColumn - 1, ' ') << "^" << std::endl;
                 
                 STORM_LOG_THROW(false, storm::exceptions::WrongFormatException, stream.str());
                 return qi::fail;