diff --git a/include/Lexesis/re.h b/include/Lexesis/re.h
index 6625339..60875b8 100644
--- a/include/Lexesis/re.h
+++ b/include/Lexesis/re.h
@@ -78,7 +78,7 @@ namespace lxs {
             std::shared_ptr<RE> e, f;
     };
 
-    std::shared_ptr<RE> parseRE(std::string& input);
+    std::shared_ptr<RE> parseRE(const std::string& input);
 
     class SyntaxError : public std::runtime_error
     {
diff --git a/src/re.cpp b/src/re.cpp
index 84318b4..86757fe 100644
--- a/src/re.cpp
+++ b/src/re.cpp
@@ -14,7 +14,7 @@ namespace lxs {
 
     State EmptyRE::toENFA(ENFA& enfa, State attach)
     {
-        enfa.numStates = std::max(attach + 1, enfa.numStates);
+        enfa.numStates = attach + 1;
         enfa.accepting.clear();
         enfa.accepting.insert(attach + 1);
         return attach + 1;
@@ -134,6 +134,7 @@ namespace lxs {
                 case '.':
                 case '\'':
                 case '"':
+                case '-':
                     break;
                 case 'n':
                     c = '\n'; break;
@@ -159,23 +160,24 @@ namespace lxs {
 
         void sumREs(std::vector<std::shared_ptr<RE> >& res)
         {
-            for (std::size_t step = 2; step < res.size(); step <<= 1)
+            for (std::size_t step = 1; step < res.size(); step <<= 1)
             {
-                for (std::size_t i = 0; i < res.size(); i += step)
+                for (std::size_t i = 0; i < res.size(); i += step * 2)
                 {
-                    if (i + step / 2 < res.size())
-                        res[i] = std::make_shared<PlusRE>(res[i], res[i + step / 2]);
+                    if (i + step < res.size())
+                        res[i] = std::make_shared<PlusRE>(res[i], res[i + step]);
                 }
             }
         }
 
-        std::shared_ptr<RE> parseCharacterClass(string& input, size_t& idx) {
+        std::shared_ptr<RE> parseCharacterClass(const string& input, size_t& idx) {
             if (idx >= input.size())
                 throw SyntaxError("Unclosed character class");
             std::vector<std::shared_ptr<RE> > chars;
             std::set<char> used_chars;
 
             bool invert = false;
+            int last_char = -1;
 
             if (input[idx] == '^')
             {
@@ -191,6 +193,7 @@ namespace lxs {
             {
                 used_chars.insert(']');
                 idx++;
+                last_char = ']';
             }
             
             if (idx >= input.size())
@@ -200,6 +203,7 @@ namespace lxs {
             {
                 used_chars.insert('-');
                 idx++;
+                last_char = '-';
             }
 
             if (idx >= input.size())
@@ -220,10 +224,13 @@ namespace lxs {
                     }
                     else
                     {
-                        for (int i = ((SingleRE*)(chars[chars.size() - 1].get()))->c + 1; i <= input[idx]; i++)
+                        if (last_char == -1)
+                            throw SyntaxError("Nothing to apply range to");
+                        for (int i = last_char + 1; i <= input[idx]; i++)
                         {
                             used_chars.insert((char) i);
                         }
+                        last_char = -1;
                     }
                 }
                 else if (input[idx] == '\\')
@@ -231,11 +238,13 @@ namespace lxs {
                     idx++;
                     if (idx >= input.size())
                         throw SyntaxError("Unclosed character classe");
-                    used_chars.insert(parseEscapeChar(input[idx]));
+                    last_char = parseEscapeChar(input[idx]);
+                    used_chars.insert(last_char);
                 }
                 else
                 {
                     used_chars.insert(input[idx]);
+                    last_char = input[idx];
                 }
             }
             
@@ -263,7 +272,7 @@ namespace lxs {
             return any[0];
         }
 
-        std::shared_ptr<RE> parseRE(string& input, size_t& idx)
+        std::shared_ptr<RE> parseRE(const string& input, size_t& idx)
         {
             stack<std::shared_ptr<RE> > stk;
             for (; idx < input.length(); idx++)
@@ -358,7 +367,7 @@ namespace lxs {
 
     }
 
-    std::shared_ptr<RE> parseRE(string& input)
+    std::shared_ptr<RE> parseRE(const string& input)
     {
         size_t i = 0;
         std::shared_ptr<RE> res = parseRE(input, i);