diff --git a/ChangeLog b/ChangeLog
index 24efca2da..3686acaa9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -87,6 +87,11 @@ FlexibleSUSY 2.0.0 [not released yet]
 
 FlexibleSUSY-1.7.3 [not released yet]
 
+ * Change (commit 43bb03a): FlexibleSUSY now aborts the code
+   generation if the user tries to fix an unknown parameter in a
+   constraint.  (Before this commit, FlexibleSUSY did only print a
+   warning.)
+
  * Bugfix (commit 4a5ada7): Adding missing return statement in
    function recalculate_mw_pole().  This bug was only present if the W
    pole mass is used as input (not GF).
diff --git a/doc/images/FS-models.xcf b/doc/images/FS-models.xcf
index c8138643a..2d2976552 100644
Binary files a/doc/images/FS-models.xcf and b/doc/images/FS-models.xcf differ
diff --git a/meta/Constraint.m b/meta/Constraint.m
index 119d909e4..c5d1a0e14 100644
--- a/meta/Constraint.m
+++ b/meta/Constraint.m
@@ -25,8 +25,6 @@
 
 SetTemporarily::usage="set temporary variables";
 
-ResetTemporarily::usage="set temporary variables";
-
 Begin["`Private`"];
 
 allBetaFunctions = {};
@@ -43,7 +41,9 @@
           Parameters`IsExtraParameter[parameter],
           Parameters`SetParameter[parameter, value, modelPrefix],
           True,
-          Print["Error: ", parameter, " is neither a model nor an input parameter!"];
+          Print["Error: ", parameter, " cannot be set in the constraint,",
+                " because it is neither a model nor an input parameter!"];
+          Quit[1];
           ""
          ];
 
@@ -599,30 +599,30 @@
     Parameters`CreateLocalConstRefs[pars] <> "\n" <>
     StringJoin[CheckPerturbativityForParameter[#,thresh]& /@ pars];
 
-SaveValue[par_[idx__], prefix_String] :=
+SaveValue[par_[idx__]] :=
     Module[{parStr = CConversion`ToValidCSymbolString[par],
-            parStrIdx = CConversion`ToValidCSymbolString[par[idx]]},
-           "const auto " <> prefix <> parStrIdx <> " = MODELPARAMETER(" <> parStr <> ")" <>
-           "(" <> Utils`StringJoinWithSeparator[ToString /@ {idx},","] <> ");"
+            parStrIdx = CConversion`ToValidCSymbolString[par[idx]], oldVal},
+           oldVal = "old_" <> parStrIdx;
+           "const auto " <> oldVal <> " = MODELPARAMETER(" <> parStr <> ")" <>
+           "(" <> Utils`StringJoinWithSeparator[ToString /@ {idx},","] <> ");\n" <>
+           "const auto save_" <> parStrIdx <> " = make_raii_guard([this," <> oldVal <> "]{ " <>
+           Parameters`SetParameter[par[idx], oldVal, "MODEL->"] <> " });\n"
           ];
 
-SaveValue[par_, prefix_String] :=
-    Module[{parStr = CConversion`ToValidCSymbolString[par]},
-           "const auto " <> prefix <> parStr <> " = MODELPARAMETER(" <> parStr <> ");"
+SaveValue[par_] :=
+    Module[{parStr = CConversion`ToValidCSymbolString[par], oldVal},
+           oldVal = "old_" <> parStr;
+           "const auto " <> oldVal <> " = MODELPARAMETER(" <> parStr <> ");\n" <>
+           "const auto save_" <> parStr <> " = make_raii_guard([this," <> oldVal <> "]{ " <>
+           Parameters`SetParameter[par, oldVal, "MODEL->"] <> " });\n"
           ];
 
-RestoreValue[par_, prefix_String] :=
-    Parameters`SetParameter[
-        par,
-        prefix <> CConversion`ToValidCSymbolString[par],
-        "MODEL->"];
-
 SetTemporarily[settings_List] :=
     Module[{tempSettings = Cases[settings, {FlexibleSUSY`Temporary[p_], v_} :> {p,v}],
             set, savedVals},
            If[tempSettings === {}, Return[""];];
            set = ApplyConstraints[tempSettings];
-           savedVals = Utils`StringJoinWithSeparator[SaveValue[#[[1]], "old_"]& /@ tempSettings, "\n"];
+           savedVals = Utils`StringJoinWithSeparator[SaveValue[#[[1]]]& /@ tempSettings, "\n"];
            "// temporary parameter re-definitons\n" <>
            savedVals <> "\n{\n" <> IndentText[set] <> "}"
           ];
diff --git a/meta/FlexibleSUSY.m b/meta/FlexibleSUSY.m
index 66bd2f374..bbbd148d4 100644
--- a/meta/FlexibleSUSY.m
+++ b/meta/FlexibleSUSY.m
@@ -739,7 +739,7 @@ FlexibleSUSY model file (FlexibleSUSY.m).
                      {minimumScale_, maximumScale_}, files_List] :=
    Module[{applyConstraint = "", calculateScale, scaleGuess,
            restrictScale,
-           temporarySetting = "", temporaryResetting = "",
+           temporarySetting = "",
            setDRbarYukawaCouplings,
            calculateDRbarMasses,
            calculateDeltaAlphaEm, calculateDeltaAlphaS,
@@ -753,7 +753,6 @@ FlexibleSUSY model file (FlexibleSUSY.m).
           scaleGuess      = Constraint`CalculateScale[scaleFirstGuess, "initial_scale_guess"];
           restrictScale   = Constraint`RestrictScale[{minimumScale, maximumScale}];
           temporarySetting   = Constraint`SetTemporarily[settings];
-          temporaryResetting = Constraint`ResetTemporarily[settings];
           calculateDeltaAlphaEm   = ThresholdCorrections`CalculateDeltaAlphaEm[FlexibleSUSY`FSRenormalizationScheme];
           calculateDeltaAlphaS    = ThresholdCorrections`CalculateDeltaAlphaS[FlexibleSUSY`FSRenormalizationScheme];
           calculateThetaW         = ThresholdCorrections`CalculateThetaW[FSWeakMixingAngleOptions,SARAH`SupersymmetricModel];
@@ -791,7 +790,6 @@ FlexibleSUSY model file (FlexibleSUSY.m).
                    "@scaleGuess@"           -> IndentText[WrapLines[scaleGuess]],
                    "@restrictScale@"        -> IndentText[WrapLines[restrictScale]],
                    "@temporarySetting@"     -> IndentText[WrapLines[temporarySetting]],
-                   "@temporaryResetting@"   -> IndentText[WrapLines[temporaryResetting]],
                    "@calculateGaugeCouplings@" -> IndentText[WrapLines[calculateGaugeCouplings]],
                    "@calculateDeltaAlphaEm@" -> IndentText[WrapLines[calculateDeltaAlphaEm]],
                    "@calculateDeltaAlphaS@"  -> IndentText[WrapLines[calculateDeltaAlphaS]],
diff --git a/meta/LoopMasses.m b/meta/LoopMasses.m
index 0c0d75bdc..3839692e5 100644
--- a/meta/LoopMasses.m
+++ b/meta/LoopMasses.m
@@ -143,7 +143,7 @@
     "const double self_energy = Re(" <> selfEnergyFunction <> "(p));\n" <>
     "const double mass_sqr = " <> massMatrixName <> " - self_energy;\n\n" <>
     "if (mass_sqr < 0.)\n" <>
-    IndentText["problems.flag_pole_tachyon(" <> particleName <> ");"] <> "\n\n" <>
+    IndentText[TreeMasses`FlagPoleTachyon[particleName]] <> "\n" <>
     "PHYSICAL(" <> massName <> ") = AbsSqrt(mass_sqr);\n";
 
 
@@ -686,7 +686,7 @@ be set to the (positive) tree-level mass.  M_tree
     Module[{result, body = ""},
            If[!IsFermion[particle] &&
               !(IsUnmixed[particle] && GetMassOfUnmixedParticle[particle] === 0),
-              body = "if (!force_output && problems.is_running_tachyon(" <> ToValidCSymbolString[particle] <> "))\n" <>
+              body = "if (!force_output && problems.is_running_tachyon(" <> FlexibleSUSY`FSModelName <> "_info::" <> ToValidCSymbolString[particle] <> "))\n" <>
                      IndentText["return;"] <> "\n\n";
              ];
            body = body <> DoDiagonalization[particle, precision, tadpole];
@@ -715,7 +715,7 @@ be set to the (positive) tree-level mass.  M_tree
               Return[""];
              ];
            If[!(IsUnmixed[particle] && GetMassOfUnmixedParticle[particle] === 0),
-              body = "if (!force_output && problems.is_running_tachyon(" <> ToValidCSymbolString[particle] <> "))\n" <>
+              body = "if (!force_output && problems.is_running_tachyon(" <> FlexibleSUSY`FSModelName <> "_info::" <> ToValidCSymbolString[particle] <> "))\n" <>
                      IndentText["return 0.;"] <> "\n\n";
              ];
            If[!IsMassless[particle],
@@ -734,7 +734,7 @@ be set to the (positive) tree-level mass.  M_tree
                       "const double self_energy = Re(" <> selfEnergyFunction <> "(p));\n" <>
                       "const double mass_sqr = " <> mTree <> " - self_energy;\n\n" <>
                       "if (mass_sqr < 0.)\n" <>
-                      IndentText["problems.flag_pole_tachyon(" <> particleName <> ");"] <> "\n\n" <>
+                      IndentText[TreeMasses`FlagPoleTachyon[particleName]] <> "\n" <>
                       "return AbsSqrt(mass_sqr);\n";
               ,
               body = "return 0.;\n";
@@ -1085,7 +1085,7 @@ be set to the (positive) tree-level mass.  M_tree
               "const double self_energy = Re(" <> selfEnergyFunction <> "(p));\n" <>
               "const double mass_sqr = Sqr(m_pole) + self_energy;\n\n" <>
               "if (mass_sqr < 0.) {\n" <>
-              IndentText["problems.flag_running_tachyon(" <> particleName <> ");\n" <>
+              IndentText[TreeMasses`FlagPoleTachyon[particleName] <>
                          "return m_pole;"] <> "\n}\n\n" <>
               "return AbsSqrt(mass_sqr);\n";
              ];
diff --git a/meta/SelfEnergies.m b/meta/SelfEnergies.m
index adc2d1c67..adf65f539 100644
--- a/meta/SelfEnergies.m
+++ b/meta/SelfEnergies.m
@@ -589,8 +589,12 @@
 DivideTadpoleByVEV[higgsAndVEV_List, arrayName_String] :=
     Module[{body = "", v, vev},
            For[v = 1, v <= Length[higgsAndVEV], v++,
-               vev = CConversion`RValueToCFormString[higgsAndVEV[[v,3]]];
-               body = body <> arrayName <> "[" <> ToString[v-1] <> "] /= " <> vev <> ";\n";
+               vev = higgsAndVEV[[v,3]];
+               If[vev === 0,
+                  body = body <> arrayName <> "[" <> ToString[v-1] <> "] = 0.;\n";,
+                  vev = CConversion`RValueToCFormString[vev];
+                  body = body <> arrayName <> "[" <> ToString[v-1] <> "] /= " <> vev <> ";\n";
+                 ];
               ];
            body
           ];
diff --git a/meta/ThresholdCorrections.m b/meta/ThresholdCorrections.m
index 77456129d..7325a37c8 100644
--- a/meta/ThresholdCorrections.m
+++ b/meta/ThresholdCorrections.m
@@ -601,8 +601,7 @@
 const double mw_pole_sqr = Sqr(mw_drbar) - self_energy_w_at_mw;
 
 if (mw_pole_sqr < 0.)
-   MODEL->get_problems().flag_pole_tachyon(" <> FlexibleSUSY`FSModelName <> "_info::" <> wStr <> ");
-
+   " <> TreeMasses`FlagPoleTachyon[wStr, "MODEL->get_problems()."] <> "
 return AbsSqrt(mw_pole_sqr);"
           ];
 
diff --git a/meta/TreeMasses.m b/meta/TreeMasses.m
index e7b25673c..f543b3af3 100644
--- a/meta/TreeMasses.m
+++ b/meta/TreeMasses.m
@@ -198,6 +198,9 @@
 CallDiagonalizeSymmetricFunction::usage="";
 CallDiagonalizeHermitianFunction::usage="";
 
+FlagPoleTachyon::usage = "";
+FlagRunningTachyon::usage = "";
+
 Begin["`Private`"];
 
 unrotatedParticles = {};
@@ -1250,7 +1253,7 @@ the fundamental representation of SU(3) in SARAH.
            WrapMacro[CConversion`ToValidCSymbolString[FlexibleSUSY`M[particle]],macro] <>
            If[dimEnd > 1, ".tail<" <> ToString[dimEnd - dimStart + 1] <> ">().minCoeff()", ""]<>
            " < 0.) " <>
-           "problems.flag_pole_tachyon(" <> particleName <> ");\n"
+           FlagPoleTachyon[particleName]
           ];
 
 CheckPoleMassesForTachyons[macro_String] :=
@@ -1338,20 +1341,25 @@ the fundamental representation of SU(3) in SARAH.
            {prototype, def}
           ];
 
-FlagTachyon[particle_String] :=
-    "problems.flag_running_tachyon(" <>
+FlagPoleTachyon[particle_String, problems_String:"problems."] :=
+    problems <> "flag_pole_tachyon(" <>
+    FlexibleSUSY`FSModelName <> "_info::" <> particle <>
+    ");\n";
+
+FlagRunningTachyon[particle_String, problems_String:"problems."] :=
+    problems <> "flag_running_tachyon(" <>
     FlexibleSUSY`FSModelName <> "_info::" <> particle <>
     ");\n";
 
-FlagTachyon[particles_List] :=
-    StringJoin[FlagTachyon /@ particles];
+FlagRunningTachyon[particles_List] :=
+    StringJoin[FlagRunningTachyon /@ particles];
 
-FlagTachyon[particle_] :=
-    FlagTachyon[ToValidCSymbolString[GetHead[particle]]];
+FlagRunningTachyon[particle_] :=
+    FlagRunningTachyon[ToValidCSymbolString[GetHead[particle]]];
 
-CheckTachyon[particle_, eigenvector_String] :=
+CheckRunningTachyon[particle_, eigenvector_String] :=
     "if (" <> eigenvector <> If[GetDimension[particle] > 1, ".minCoeff()", ""] <> " < 0.) {\n" <>
-    IndentText[FlagTachyon[particle]] <>
+    IndentText[FlagRunningTachyon[particle]] <>
     "}\n";
 
 FlagBadMass[particle_String, eigenvalue_String] :=
@@ -1473,7 +1481,7 @@ the fundamental representation of SU(3) in SARAH.
               body = body <> "\n" <>
                      IndentText[
                          If[ContainsMassless[eigenVector], "",
-                            CheckTachyon[eigenVector, ev] <> "\n"] <>
+                            CheckRunningTachyon[eigenVector, ev] <> "\n"] <>
                          ev <> " = AbsSqrt(" <> ev <> ");\n"
                      ];
              ];
@@ -1541,7 +1549,7 @@ the fundamental representation of SU(3) in SARAH.
               !IsMassless[massESSymbol],
               body = body <> "\n" <>
                      If[ContainsMassless[eigenVector], "",
-                        CheckTachyon[massESSymbol, ev] <> "\n"] <>
+                        CheckRunningTachyon[massESSymbol, ev] <> "\n"] <>
                      ev <> " = AbsSqrt(" <> ev <> ");\n";
              ];
            body = IndentText[body];
diff --git a/src/raii.hpp b/src/raii.hpp
index f6795b50b..57968a89e 100644
--- a/src/raii.hpp
+++ b/src/raii.hpp
@@ -29,7 +29,11 @@ template <typename T>
 class RAII_save {
 public:
    RAII_save(T& var_) noexcept : var(var_), value(var_) {}
+   RAII_save(const RAII_save&) = delete;
+   RAII_save(RAII_save&&) = default;
    ~RAII_save() { var = value; }
+   RAII_save& operator=(const RAII_save&) = delete;
+   RAII_save& operator=(RAII_save&& other) = default;
 
 private:
    T& var;
diff --git a/templates/mass_eigenstates.cpp.in b/templates/mass_eigenstates.cpp.in
index 3150bae19..3dde26fe0 100644
--- a/templates/mass_eigenstates.cpp.in
+++ b/templates/mass_eigenstates.cpp.in
@@ -57,8 +57,6 @@
 
 namespace flexiblesusy {
 
-using namespace @ModelName@_info;
-
 #define CLASSNAME @ModelName@_mass_eigenstates
 
 #define PHYSICAL(parameter) physical.parameter
diff --git a/templates/two_scale_high_scale_constraint.cpp.in b/templates/two_scale_high_scale_constraint.cpp.in
index 2ef81fbd7..0ad0e4d4d 100644
--- a/templates/two_scale_high_scale_constraint.cpp.in
+++ b/templates/two_scale_high_scale_constraint.cpp.in
@@ -26,6 +26,7 @@
 #include "ew_input.hpp"
 #include "gsl_utils.hpp"
 #include "minimizer.hpp"
+#include "raii.hpp"
 #include "root_finder.hpp"
 #include "threshold_loop_functions.hpp"
 #include "numerics2.hpp"
@@ -75,8 +76,6 @@ void @ModelName@_high_scale_constraint<Two_scale>::apply()
 @applyConstraint@
 
    check_non_perturbative();
-
-@temporaryResetting@
 }
 
 bool @ModelName@_high_scale_constraint<Two_scale>::check_non_perturbative()
diff --git a/templates/two_scale_low_scale_constraint.cpp.in b/templates/two_scale_low_scale_constraint.cpp.in
index 2b06f9069..d9a5caa39 100644
--- a/templates/two_scale_low_scale_constraint.cpp.in
+++ b/templates/two_scale_low_scale_constraint.cpp.in
@@ -27,6 +27,7 @@
 #include "ew_input.hpp"
 #include "gsl_utils.hpp"
 #include "minimizer.hpp"
+#include "raii.hpp"
 #include "root_finder.hpp"
 #include "threshold_loop_functions.hpp"
 #include "weinberg_angle.hpp"
@@ -86,8 +87,6 @@ void @ModelName@_low_scale_constraint<Two_scale>::apply()
 
    if (model->get_thresholds())
       qedqcd.setPoleMW(recalculate_mw_pole(qedqcd.displayPoleMW()));
-
-@temporaryResetting@
 }
 
 const Eigen::Matrix<std::complex<double>,3,3>& @ModelName@_low_scale_constraint<Two_scale>::get_ckm()
diff --git a/templates/two_scale_model.cpp.in b/templates/two_scale_model.cpp.in
index 4a5574131..444dc40e9 100644
--- a/templates/two_scale_model.cpp.in
+++ b/templates/two_scale_model.cpp.in
@@ -34,8 +34,6 @@
 
 namespace flexiblesusy {
 
-using namespace @ModelName@_info;
-
 #define CLASSNAME @ModelName@<Two_scale>
 
 CLASSNAME::@ModelName@(const @ModelName@_input_parameters& input_)
diff --git a/templates/two_scale_susy_scale_constraint.cpp.in b/templates/two_scale_susy_scale_constraint.cpp.in
index 4fff95211..4f9436665 100644
--- a/templates/two_scale_susy_scale_constraint.cpp.in
+++ b/templates/two_scale_susy_scale_constraint.cpp.in
@@ -26,6 +26,7 @@
 #include "ew_input.hpp"
 #include "gsl_utils.hpp"
 #include "minimizer.hpp"
+#include "raii.hpp"
 #include "root_finder.hpp"
 #include "threshold_loop_functions.hpp"
 
@@ -73,7 +74,6 @@ void @ModelName@_susy_scale_constraint<Two_scale>::apply()
 
    // apply user-defined susy scale constraints
 @applyConstraint@
-@temporaryResetting@
 }
 
 double @ModelName@_susy_scale_constraint<Two_scale>::get_scale() const