diff --git a/include/parse.hpp b/include/parse.hpp
index ab2381e..cce2f05 100644
--- a/include/parse.hpp
+++ b/include/parse.hpp
@@ -6,6 +6,7 @@
 #include <string>
 #include <utility>
 #include <vector>
+#include <set>
 #include <tuple>
 
 #define SPACES          " \t"
@@ -37,9 +38,9 @@ struct list_parse_options {
 };
 
 // globals
-
-extern const std::vector<std::string> posix_cmdvar;
-extern const std::vector<std::string> bash_cmdvar;
+extern const std::set<std::string> all_reserved_words;
+extern const std::set<std::string> posix_cmdvar;
+extern const std::set<std::string> bash_cmdvar;
 
 std::string import_file(std::string const& path);
 
diff --git a/include/util.hpp b/include/util.hpp
index f1fc52d..0533bd5 100644
--- a/include/util.hpp
+++ b/include/util.hpp
@@ -24,8 +24,6 @@ inline bool is_dev_file(std::string const& filename) { return filename.substr(0,
 
 std::string indent(int n);
 
-bool is_among(std::string const& in, std::vector<std::string> const& values);
-
 std::vector<std::string> split(std::string const& in, const char* splitters);
 std::vector<std::string> split(std::string const& in, char c);
 
@@ -137,6 +135,12 @@ bool is_in_vector(T el, std::vector<T> vec)
   return false;
 }
 
+template <class T>
+bool is_in_set(T el, std::set<T> ss)
+{
+  return ss.find(el) != ss.end();
+}
+
 std::set<std::string> prune_matching(std::set<std::string>& in, std::regex re);
 
 std::string delete_brackets(std::string const& in);
diff --git a/src/minify.cpp b/src/minify.cpp
index 5c142e4..4c5295e 100644
--- a/src/minify.cpp
+++ b/src/minify.cpp
@@ -310,6 +310,7 @@ void minify_fct(_obj* in, std::regex const& exclude)
   concat_sets(allcmds, m_excluded_fct);
   concat_sets(allcmds, unsets);
   // create mapping
+  concat_sets(allcmds, all_reserved_words);
   fctmap=gen_minimal_map(m_fcts, allcmds);
   // perform replace
   recurse(r_replace_fct, in, &fctmap);
diff --git a/src/parse.cpp b/src/parse.cpp
index 13d88cb..e8a64a0 100644
--- a/src/parse.cpp
+++ b/src/parse.cpp
@@ -14,14 +14,14 @@
 // macro
 
 // constants
-const std::vector<std::string> posix_cmdvar = { "export", "unset", "local", "read", "getopts" };
-const std::vector<std::string> bash_cmdvar  = { "readonly", "declare", "typeset" };
+const std::set<std::string> posix_cmdvar = { "export", "unset", "local", "read", "getopts" };
+const std::set<std::string> bash_cmdvar  = { "readonly", "declare", "typeset" };
 
-const std::vector<std::string> arithmetic_precedence_operators = { "!", "~", "+", "-" };
-const std::vector<std::string> arithmetic_operators = { "+", "-", "*", "/", "+=", "-=", "*=", "/=", "=", "==", "!=", "&", "|", "^", "<<", ">>", "&&", "||" };
+const std::set<std::string> arithmetic_precedence_operators = { "!", "~", "+", "-" };
+const std::set<std::string> arithmetic_operators = { "+", "-", "*", "/", "+=", "-=", "*=", "/=", "=", "==", "!=", "&", "|", "^", "<<", ">>", "&&", "||" };
 
-const std::vector<std::string> all_reserved_words = { "if", "then", "else", "fi", "case", "esac", "for", "while", "do", "done", "{", "}" };
-const std::vector<std::string> out_reserved_words = { "then", "else", "fi", "esac", "do", "done", "}" };
+const std::set<std::string> all_reserved_words = { "if", "then", "else", "fi", "case", "esac", "for", "while", "do", "done", "{", "}" };
+const std::set<std::string> out_reserved_words = { "then", "else", "fi", "esac", "do", "done", "}" };
 
 // stuff
 
@@ -276,7 +276,7 @@ std::pair<arithmetic*, parse_context> parse_arithmetic(parse_context ctx)
   }
 
   auto po = get_operator(ctx);
-  if(is_among(po.first, arithmetic_precedence_operators))
+  if(is_in_set(po.first, arithmetic_precedence_operators))
   {
     ctx.i = po.second;
     auto pa = parse_arithmetic(ctx);
@@ -335,7 +335,7 @@ std::pair<arithmetic*, parse_context> parse_arithmetic(parse_context ctx)
     auto po = get_operator(ctx);
     if(po.first != "")
     {
-      if(!is_among(po.first, arithmetic_operators))
+      if(!is_in_set(po.first, arithmetic_operators))
       {
         parse_error( "Unknown arithmetic operator: "+po.first, ctx);
       }
@@ -1289,9 +1289,10 @@ std::pair<cmd*, parse_context> parse_cmd(parse_context ctx)
   ctx = parse_cmd_varassigns(ret, ctx);
 
   auto wp=get_word(ctx, ARG_END);
-  if(is_in_vector(wp.first, posix_cmdvar) || is_in_vector(wp.first, bash_cmdvar))
+  bool is_bash_cmdvar=false;
+  if(is_in_set(wp.first, posix_cmdvar) || (is_bash_cmdvar=is_in_set(wp.first, bash_cmdvar)) )
   {
-    if(!ctx.bash && is_in_vector(wp.first, bash_cmdvar))
+    if(!ctx.bash && (is_bash_cmdvar || is_in_set(wp.first, bash_cmdvar)))
     {
       parse_error("bash specific: "+wp.first, ctx);
     }
@@ -1627,7 +1628,7 @@ std::pair<block*, parse_context> parse_block(parse_context ctx)
       ret = pp.first;
       ctx = pp.second;
     }
-    else if(is_in_vector(word, out_reserved_words)) // is a reserved word
+    else if(is_in_set(word, out_reserved_words)) // is a reserved word
     {
       parse_error( strf("Unexpected '%s'", word.c_str())+expecting(ctx.expecting) , ctx);
       ctx.i+=word.size();
diff --git a/src/processing.cpp b/src/processing.cpp
index 217e98a..ace54c4 100644
--- a/src/processing.cpp
+++ b/src/processing.cpp
@@ -160,7 +160,7 @@ std::string get_varname(arg* in)
 
 bool cmd_is_argvar(std::string const& in)
 {
-  return is_in_vector(in, posix_cmdvar) || is_in_vector(in, bash_cmdvar);
+  return is_in_set(in, posix_cmdvar) || is_in_set(in, bash_cmdvar);
 }
 
 bool cmd::is_argvar()
diff --git a/src/util.cpp b/src/util.cpp
index 18a1520..bea1a46 100644
--- a/src/util.cpp
+++ b/src/util.cpp
@@ -45,14 +45,6 @@ std::string dirname(std::string const& in)
     return ".";
 }
 
-bool is_among(std::string const& in, std::vector<std::string> const& values)
-{
-  for(auto it: values)
-    if(in == it)
-      return true;
-  return false;
-}
-
 std::vector<std::string> split(std::string const& in, const char* splitters)
 {
   uint32_t i=0,j=0;