Fix conversion warning

Eigen/src/Core/util/IntegralConstant.h

diff --git a/Eigen/src/Core/util/IntegralConstant.h b/Eigen/src/Core/util/IntegralConstant.h
index 78a4705..bf99cd8 100644
--- a/Eigen/src/Core/util/IntegralConstant.h
+++ b/Eigen/src/Core/util/IntegralConstant.h
@@ -192,7 +192,7 @@
 // The generic typename T is mandatory. Otherwise, a code like fix<N> could refer to either the function above or this next overload.
 // This way a code like fix<N> can only refer to the previous function.
 template<int N,typename T>
-inline internal::VariableAndFixedInt<N> fix(T val) { return internal::VariableAndFixedInt<N>(val); }
+inline internal::VariableAndFixedInt<N> fix(T val) { return internal::VariableAndFixedInt<N>(internal::convert_index<int>(val)); }
 #endif
 
 #else // EIGEN_PARSED_BY_DOXYGEN