diff --git a/multichoose.h b/multichoose.h
index 51acb24..1e19a69 100644
--- a/multichoose.h
+++ b/multichoose.h
@@ -1,7 +1,7 @@
 #ifndef __MULTICHOOSE_H
 #define __MULTICHOOSE_H
 
-/* 
+/*
 
 multichoose.h  -- n multichoose k for generic vectors
 
@@ -58,7 +58,10 @@ std::vector< std::vector<T> > multichoose(int k, std::vector<T>& objects) {
             multiset.push_back(*a[i]);
         choices.push_back(multiset);
         j=k;
-        do { j--; } while(a[j]==b[j]);
+        do {
+	    j--;
+	    if (j<0) break;
+	} while(a[j]==b[j]);
         if (j<0) break;
         j_1=j;
         while(j_1<=k-1){
@@ -72,7 +75,7 @@ std::vector< std::vector<T> > multichoose(int k, std::vector<T>& objects) {
             j_1=q;
         }
     }
-    
+
     return choices;
 }