diff --git a/Changes b/Changes
index a09dc54..8cfb3d1 100644
--- a/Changes
+++ b/Changes
@@ -1,6 +1,8 @@
-0.36 2020-06-16
+0.36 2020-07-15
     - [security] Upgraded version of Google Guava
       (CVE-2018-10237; diewald)
+    - Optimize regular expressions to use character classes
+      instead of alternations (kupietz)
 
 0.35 2019-11-12
     - Added a method to add warnings in QuerySerializer (margaretha)
diff --git a/src/main/java/de/ids_mannheim/korap/query/serialize/Cosmas2QueryProcessor.java b/src/main/java/de/ids_mannheim/korap/query/serialize/Cosmas2QueryProcessor.java
index 4bc806a..1ce1635 100644
--- a/src/main/java/de/ids_mannheim/korap/query/serialize/Cosmas2QueryProcessor.java
+++ b/src/main/java/de/ids_mannheim/korap/query/serialize/Cosmas2QueryProcessor.java
@@ -800,7 +800,7 @@
 
     private void processOPLABEL (Tree node) {
         // Step I: create element
-        String key = node.getChild(0).toStringTree().replaceAll("<|>", "");
+        String key = node.getChild(0).toStringTree().replaceAll("[<>]", "");
         Map<String, Object> elem = KoralObjectGenerator.makeSpan(key);
         // Step II: decide where to put
         putIntoSuperObject(elem);
@@ -1539,7 +1539,7 @@
      * Normalises position operators to equivalents using #BED
      */
     private String rewritePositionQuery (String q) {
-        Pattern p = Pattern.compile("(\\w+):((\\+|-)?(sa|se|pa|pe|ta|te),?)+");
+        Pattern p = Pattern.compile("(\\w+):(([+\\-])?(sa|se|pa|pe|ta|te),?)+");
         Matcher m = p.matcher(q);
 
         String rewrittenQuery = q;
@@ -1547,7 +1547,7 @@
             String match = m.group();
             String conditionsString = match.split(":")[1];
             Pattern conditionPattern =
-                    Pattern.compile("(\\+|-)?(sa|se|pa|pe|ta|te)");
+                    Pattern.compile("([+\\-])?(sa|se|pa|pe|ta|te)");
             Matcher conditionMatcher =
                     conditionPattern.matcher(conditionsString);
             String replacement = "#BED(" + m.group(1) + " , ";
diff --git a/src/main/java/de/ids_mannheim/korap/query/serialize/QueryUtils.java b/src/main/java/de/ids_mannheim/korap/query/serialize/QueryUtils.java
index 47b5e09..84932e8 100644
--- a/src/main/java/de/ids_mannheim/korap/query/serialize/QueryUtils.java
+++ b/src/main/java/de/ids_mannheim/korap/query/serialize/QueryUtils.java
@@ -211,7 +211,7 @@
     public static String escapeRegexSpecialChars (String key) {
         key.replace("\\", "\\\\");
         Pattern p = Pattern
-                .compile("\\.|\\^|\\$|\\||\\?|\\*|\\+|\\(|\\)|\\[|\\]|\\{|\\}");
+                .compile("[.^$|?*+()\\[\\]{}]");
         Matcher m = p.matcher(key);
         while (m.find()) {
             String match = m.group();