diff --git a/app/src/main/java/ch/nuth/zhaw/exbox/BracketServer.java b/app/src/main/java/ch/nuth/zhaw/exbox/BracketServer.java
index 13490d6..0f9f480 100644
--- a/app/src/main/java/ch/nuth/zhaw/exbox/BracketServer.java
+++ b/app/src/main/java/ch/nuth/zhaw/exbox/BracketServer.java
@@ -37,7 +37,9 @@ public class BracketServer implements CommandExecutor {
         for (MatchResult result : results) {
             if (bracketPairs.keySet().contains(result.group())) {
                 openBrackets.push(result.group());
-            } else if (result.group().equals(bracketPairs.get(openBrackets.peek()))) {
+            } else if (
+                !openBrackets.isEmpty() &&
+                result.group().equals(bracketPairs.get(openBrackets.peek()))) {
                 openBrackets.pop();
             } else {
                 return false;