diff --git a/include/tc/core.hpp b/include/tc/core.hpp
index 147935c..b8cfd4e 100644
--- a/include/tc/core.hpp
+++ b/include/tc/core.hpp
@@ -115,10 +115,10 @@ namespace tc {
     };
 
     struct SubGroup : public Group {
-        const std::vector<int> gen_map;
+        std::vector<int> gen_map;
         const Group &parent;
 
-        SubGroup(const Group &parent, const std::vector<int> &gen_map);
+        SubGroup(const Group &parent, std::vector<int> gen_map);
     };
 
     Group operator*(const Group &g, const Group &h);
diff --git a/src/core.cpp b/src/core.cpp
index 00346b0..5dbe99b 100644
--- a/src/core.cpp
+++ b/src/core.cpp
@@ -136,8 +136,11 @@ namespace tc {
         return g;
     }
 
-    SubGroup::SubGroup(const Group &parent, const std::vector<int> &gen_map)
-        : Group(gen_map.size()), parent(parent), gen_map(gen_map) {
+    SubGroup::SubGroup(const Group &parent, std::vector<int> gen_map)
+        : Group(gen_map.size()), parent(parent) {
+
+        std::sort(gen_map.begin(), gen_map.end());
+        this->gen_map = gen_map;
 
         for (size_t i = 0; i < gen_map.size(); ++i) {
             for (size_t j = 0; j < gen_map.size(); ++j) {
diff --git a/src/solve.cpp b/src/solve.cpp
index f56f51a..948eec2 100644
--- a/src/solve.cpp
+++ b/src/solve.cpp
@@ -67,6 +67,11 @@ namespace tc {
     Cosets Group::solve(const std::vector<int> &sub_gens) const {
         Cosets cosets(ngens);
         cosets.add_row();
+
+        if (ngens == 0) {
+            return cosets;
+        }
+
         for (int g : sub_gens) {
             cosets.put(g, 0);
         }