diff --git a/common/Array.hpp b/common/Array.hpp
index 048e83e3..1bdb33a5 100644
--- a/common/Array.hpp
+++ b/common/Array.hpp
@@ -1064,10 +1064,11 @@ Array<TYPE, FUN> Array<TYPE, FUN>::reverseDim() const
 template<class TYPE, class FUN>
 Array<TYPE, FUN> Array<TYPE, FUN>::coarsen( const Array<TYPE, FUN> &filter ) const
 {
-    size_t S2 = size();
+    auto S2 = size();
     for ( size_t i = 0; i < S2.size(); i++ ) {
-        S2[i] /= filter.size( i );
-        if ( S2[i] * filter.size( i ) != size( i ) )
+    	size_t S2_i=S2[i];
+        S2_i /= filter.size( i );
+        if ( S2_i * filter.size( i ) != size( i ) )
             throw std::invalid_argument( "Array must be multiple of filter size" );
     }
     Array<TYPE, FUN> y( S2 );