diff --git a/math/minuit2/inc/Minuit2/ABObj.h b/math/minuit2/inc/Minuit2/ABObj.h
index 38ac37d15904a624c3d229cf7124f2e62661554f..e8029243bf14b35753f000e632878e485f079493 100644
--- a/math/minuit2/inc/Minuit2/ABObj.h
+++ b/math/minuit2/inc/Minuit2/ABObj.h
@@ -70,7 +70,7 @@ public:
 
 private:
 
-  ABObj& operator=(const ABObj&) {return *this;}
+  ABObj& operator=(const ABObj&) = delete;
 
 public:
 
diff --git a/math/minuit2/inc/Minuit2/MinosError.h b/math/minuit2/inc/Minuit2/MinosError.h
index 2b695ad5fe66d672e460295c10e993079d305c87..5a4516929ff2df7c53a8dcd58814b6d948456f28 100644
--- a/math/minuit2/inc/Minuit2/MinosError.h
+++ b/math/minuit2/inc/Minuit2/MinosError.h
@@ -34,6 +34,8 @@ public:
 
    MinosError(const MinosError& err) : fParameter(err.fParameter), fMinValue(err.fMinValue), fUpper(err.fUpper),  fLower(err.fLower) {}
 
+   MinosError& operator=(const MinosError& ) = default;
+
    MinosError& operator()(const MinosError& err) {
       fParameter = err.fParameter;
       fMinValue = err.fMinValue;
diff --git a/math/minuit2/inc/Minuit2/MnCross.h b/math/minuit2/inc/Minuit2/MnCross.h
index 61bd3dcf1fdea73a8e7063a0bdcb4d000cacbb53..a6b4195886420e487dd50783f3aa58d0c19bf2fa 100644
--- a/math/minuit2/inc/Minuit2/MnCross.h
+++ b/math/minuit2/inc/Minuit2/MnCross.h
@@ -45,6 +45,8 @@ public:
 
   MnCross(const MnCross& cross) : fValue(cross.fValue), fState(cross.fState), fNFcn(cross.fNFcn), fValid(cross.fValid), fLimset(cross.fLimset), fMaxFcn(cross.fMaxFcn), fNewMin(cross.fNewMin) {}
 
+  MnCross& operator=(const MnCross&) = default;
+
   MnCross& operator()(const MnCross& cross) {
     fValue = cross.fValue;
     fState = cross.fState;