diff --git a/Eigen/src/Core/ArrayBase.h b/Eigen/src/Core/ArrayBase.h
index c53ea0a4f..36bf71dde 100644
--- a/Eigen/src/Core/ArrayBase.h
+++ b/Eigen/src/Core/ArrayBase.h
@@ -169,9 +169,11 @@ template<typename Derived> class ArrayBase
     template<typename OtherDerived> explicit ArrayBase(const ArrayBase<OtherDerived>&);
   protected:
     // mixing arrays and matrices is not legal
-    template<typename OtherDerived> Derived& operator+=(const MatrixBase<OtherDerived>& mat);
+    template<typename OtherDerived> Derived& operator+=(const MatrixBase<OtherDerived>& mat)
+    {EIGEN_STATIC_ASSERT(sizeof(typename OtherDerived::Scalar)==-1,YOU_CANNOT_MIX_ARRAYS_AND_MATRICES);}
     // mixing arrays and matrices is not legal
-    template<typename OtherDerived> Derived& operator-=(const MatrixBase<OtherDerived>& mat);
+    template<typename OtherDerived> Derived& operator-=(const MatrixBase<OtherDerived>& mat)
+    {EIGEN_STATIC_ASSERT(sizeof(typename OtherDerived::Scalar)==-1,YOU_CANNOT_MIX_ARRAYS_AND_MATRICES);}
 };
 
 /** replaces \c *this by \c *this - \a other.
diff --git a/Eigen/src/Core/MatrixBase.h b/Eigen/src/Core/MatrixBase.h
index 1b0784c2b..a05614d1b 100644
--- a/Eigen/src/Core/MatrixBase.h
+++ b/Eigen/src/Core/MatrixBase.h
@@ -429,9 +429,11 @@ template<typename Derived> class MatrixBase
     template<typename OtherDerived> explicit MatrixBase(const MatrixBase<OtherDerived>&);
   protected:
     // mixing arrays and matrices is not legal
-    template<typename OtherDerived> Derived& operator+=(const ArrayBase<OtherDerived>& array);
+    template<typename OtherDerived> Derived& operator+=(const ArrayBase<OtherDerived>& array)
+    {EIGEN_STATIC_ASSERT(sizeof(typename OtherDerived::Scalar)==-1,YOU_CANNOT_MIX_ARRAYS_AND_MATRICES);}
     // mixing arrays and matrices is not legal
-    template<typename OtherDerived> Derived& operator-=(const ArrayBase<OtherDerived>& array);
+    template<typename OtherDerived> Derived& operator-=(const ArrayBase<OtherDerived>& array)
+    {EIGEN_STATIC_ASSERT(sizeof(typename OtherDerived::Scalar)==-1,YOU_CANNOT_MIX_ARRAYS_AND_MATRICES);}
 };
 
 #endif // EIGEN_MATRIXBASE_H
diff --git a/Eigen/src/Core/util/StaticAssert.h b/Eigen/src/Core/util/StaticAssert.h
index f1d9d7b3d..d285f79b1 100644
--- a/Eigen/src/Core/util/StaticAssert.h
+++ b/Eigen/src/Core/util/StaticAssert.h
@@ -87,7 +87,8 @@
         INVALID_STORAGE_ORDER_FOR_THIS_VECTOR_EXPRESSION,
         THE_BRACKET_OPERATOR_IS_ONLY_FOR_VECTORS__USE_THE_PARENTHESIS_OPERATOR_INSTEAD,
         PACKET_ACCESS_REQUIRES_TO_HAVE_INNER_STRIDE_FIXED_TO_1,
-        THIS_METHOD_IS_ONLY_FOR_SPECIFIC_TRANSFORMATIONS
+        THIS_METHOD_IS_ONLY_FOR_SPECIFIC_TRANSFORMATIONS,
+        YOU_CANNOT_MIX_ARRAYS_AND_MATRICES
       };
     };