diff --git a/fourindex.h b/fourindex.h
index f05b936..4339a24 100644
--- a/fourindex.h
+++ b/fourindex.h
@@ -716,12 +716,12 @@ if (IJ<0 || IJ>=(unsigned int)NRSMat<T>::nn || KL<0 || KL>=(unsigned int)NRSMat<
 template<class T, class DUMMY>
 T& fourindex_dense<twoelectronrealmullikan,T,DUMMY>::operator() (unsigned int i, unsigned int j, unsigned int k, unsigned int l)
 {
-unsigned int I = SMat_index_1(i,j);
-unsigned int J = SMat_index_1(k,l);
+int I = SMat_index_1(i,j);
+int J = SMat_index_1(k,l);
 //I,J act as indices of a NRSmat
 #ifdef DEBUG
      	if (*NRSMat<T>::count != 1) laerror("lval (i,j,k,l) with count > 1 in fourindex_dense");
-       	if (I<0 || I>=(unsigned int)NRSMat<T>::nn || J<0 || J>=(unsigned int)NRSMat<T>::nn) laerror("fourindex_dense index out of range");
+       	if (I<0 || I>=NRSMat<T>::nn || J<0 || J>=NRSMat<T>::nn) laerror("fourindex_dense index out of range");
        	if (!NRSMat<T>::v) laerror("access to unallocated fourindex_dense");
 #endif
 return NRSMat<T>::v[SMat_index(I,J)];
@@ -731,11 +731,11 @@ return NRSMat<T>::v[SMat_index(I,J)];
 template<class T, class DUMMY>
 const T& fourindex_dense<twoelectronrealmullikan,T,DUMMY>::operator() (unsigned int i, unsigned int j, unsigned int k, unsigned int l) const
 {
-unsigned int I = SMat_index_1(i,j);
-unsigned int J = SMat_index_1(k,l);
+int I = SMat_index_1(i,j);
+int J = SMat_index_1(k,l);
 //I,J act as indices of a NRSmat
 #ifdef DEBUG
-       	if (I<0 || I>=(unsigned int)NRSMat<T>::nn || J<0 || J>=(unsigned int)NRSMat<T>::nn) laerror("fourindex_dense index out of range");
+       	if (I<0 || I>=NRSMat<T>::nn || J<0 || J>=NRSMat<T>::nn) laerror("fourindex_dense index out of range");
        	if (!NRSMat<T>::v) laerror("access to unallocated fourindex_dense");
 #endif
 return NRSMat<T>::v[SMat_index(I,J)];
diff --git a/smat.h b/smat.h
index 2c7c15f..dfd7f91 100644
--- a/smat.h
+++ b/smat.h
@@ -336,6 +336,23 @@ inline T SMat_index_1ilej(T i, T j)
 return j*(j-1)/2+i-1;
 }
 
+//indexing for antisymmetric matrix (used by fourindex)
+
+template<typename T>
+inline T ASMat_index(T i, T j)
+{
+if(i==j) return -1;
+return (i>j) ? i*(i-1)/2+j : j*(j-1)/2+i;
+}
+
+template<typename T>
+inline T ASMat_index_1(T i, T j)
+{
+if(i==j) return -1;
+return (i>j)? (i-2)*(i-1)/2+j-1 : (j-2)*(j-1)/2+i-1;
+}
+
+
 
 // access the element, 2-dim array case
 template <typename T>