--- configure.ac.orig	2020-04-30 01:52:40.000000000 -0600
+++ configure.ac	2020-10-27 17:05:31.732729921 -0600
@@ -272,7 +272,7 @@ AC_ARG_ENABLE([cocoa],
 	[if test "$enableval" = "no"; then CONFIG_COCOA="no"; fi], [])
 
 if test "$CONFIG_COCOA" = "yes"; then
-	AC_CHECK_HEADER(CoCoA/io.H, [], [CONFIG_COCOA="no"])
+	AC_CHECK_HEADER(CoCoA/BigInt.H, [], [CONFIG_COCOA="no"])
   fi
 if test "$CONFIG_COCOA" = "yes"; then
 	save_LIBS="$LIBS"
--- configure.orig	2020-04-30 01:52:40.000000000 -0600
+++ configure	2020-10-27 17:06:22.817658796 -0600
@@ -16662,8 +16662,8 @@ fi
 
 
 if test "$CONFIG_COCOA" = "yes"; then
-	ac_fn_cxx_check_header_mongrel "$LINENO" "CoCoA/io.H" "ac_cv_header_CoCoA_io_H" "$ac_includes_default"
-if test "x$ac_cv_header_CoCoA_io_H" = xyes; then :
+	ac_fn_cxx_check_header_mongrel "$LINENO" "CoCoA/BigInt.H" "ac_cv_header_CoCoA_BigInt_H" "$ac_includes_default"
+if test "x$ac_cv_header_CoCoA_BigInt_H" = xyes; then :
 
 else
   CONFIG_COCOA="no"
--- src/TmpLESystemSolver.C.orig	2019-11-03 11:20:03.000000000 -0700
+++ src/TmpLESystemSolver.C	2020-11-12 16:15:52.906906533 -0700
@@ -29,6 +29,7 @@
 #include "CoCoA/matrix.H"
 #include "CoCoA/ring.H"
 #include "CoCoA/error.H"
+#include "CoCoA/MachineInt.H"
 
 // #include <vector> // Included by DenseMatrix.H
 using std::vector;
@@ -50,7 +51,11 @@ namespace CoCoADortmund
 
     for (size_t row = 0; row < NumRowsMSource; ++row)
       for (size_t col = 0; col < NumColsMSource; ++col)
-        SetEntry(MTarget, row, col, MSource(row, col));
+      {
+        const MachineInt rowInt(static_cast<unsigned long>(row));
+        const MachineInt colInt(static_cast<unsigned long>(col));
+        SetEntry(MTarget, row, col, MSource(rowInt, colInt));
+      }
   }
 
   // Solve the linear system M*x = b by using Gauss' algorithm
@@ -60,6 +65,7 @@ namespace CoCoADortmund
     const size_t NumColsM = NumCols(M);
     const size_t NumRowsb = NumRows(b);
     const size_t NumColsb = NumCols(b);
+    const MachineInt zInt(0);
 	
     // Dimension check
     if (NumRowsM != NumRowsb)
@@ -91,13 +97,17 @@ namespace CoCoADortmund
     size_t row = 0;
     for (size_t col = 0; col < NumColsM && row < NumRowsM; ++col)
     {
+      const MachineInt rowInt(static_cast<unsigned long>(row));
+      const MachineInt colInt(static_cast<unsigned long>(col));
+
       // Check if current column contains an element != 0
-      if (IsZero(MCopy(row, col)))
+      if (IsZero(MCopy(rowInt, colInt)))
       {
         size_t i = row+1;
         for ( ; i < NumRowsM; ++i)
         {
-          if (!IsZero(MCopy(i, col)))
+          const MachineInt iInt(static_cast<unsigned long>(i));
+          if (!IsZero(MCopy(iInt, colInt)))
           {
             // Switch MCopy and bCopy rows
             MCopy->mySwapRows(i, row);
@@ -113,13 +123,14 @@ namespace CoCoADortmund
       positions.push_back(make_pair(row, col));
 
       // Found an element != 0 in current column; apply elemination
-      c = MCopy(row, col);
+      c = MCopy(rowInt, colInt);
 
       for (size_t i = row+1; i < NumRowsM; ++i)
       {
         // Transform MCopy and bCopy
-        bCopy->myAddRowMul(i, row, -MCopy(i, col)/c);
-        MCopy->myAddRowMul(i, row, -MCopy(i, col)/c);
+        const MachineInt iInt(static_cast<unsigned long>(i));
+        bCopy->myAddRowMul(i, row, -MCopy(iInt, colInt)/c);
+        MCopy->myAddRowMul(i, row, -MCopy(iInt, colInt)/c);
       }
 
       ++row;
@@ -128,7 +139,8 @@ namespace CoCoADortmund
     // row = rank(MCopy); check if a solution for the equation system exists
     for (size_t i = row; i < NumRowsb; ++i)
     {
-      if (!IsZero(bCopy(i, 0)))
+      const MachineInt iInt(static_cast<unsigned long>(i));
+      if (!IsZero(bCopy(iInt, zInt)))
         return false;
     }
 	
@@ -138,13 +150,16 @@ namespace CoCoADortmund
     while (!positions.empty())
     {
       const size_t i = positions.back().first, j = positions.back().second;
+      const MachineInt iInt(static_cast<unsigned long>(i));
+      const MachineInt jInt(static_cast<unsigned long>(j));
 
-      RingElem x(bCopy(i, 0));
+      RingElem x(bCopy(iInt, zInt));
       for (size_t k = j + 1; k < NumColsM; ++k)
       {
-        x -= MCopy(i, k) * x0Tmp(k, 0);
+        const MachineInt kInt(static_cast<unsigned long>(k));
+        x -= MCopy(iInt, kInt) * x0Tmp(kInt, zInt);
       }
-      SetEntry(x0Tmp, j, 0, x/MCopy(i, j));
+      SetEntry(x0Tmp, j, 0, x/MCopy(iInt, jInt));
 
       positions.pop_back();
     }