diff --git a/key.core/src/main/java/de/uka/ilkd/key/proof/io/UrlRuleSource.java b/key.core/src/main/java/de/uka/ilkd/key/proof/io/UrlRuleSource.java
index f921f77d6e..5144c38971 100644
--- a/key.core/src/main/java/de/uka/ilkd/key/proof/io/UrlRuleSource.java
+++ b/key.core/src/main/java/de/uka/ilkd/key/proof/io/UrlRuleSource.java
@@ -61,11 +61,11 @@ public Path file() {
             try {
                 return Paths.get(uri);
             } catch (FileSystemNotFoundException e) {
-                URI rootFs = URI.create(StringUtil.takeUntil(uri.toString(), "\\!"));
-                String internal = StringUtil.takeAfter(uri.toString(), "\\!");
-                try (FileSystem zipfs = FileSystems.newFileSystem(rootFs, new HashMap<>())) {
-                    return zipfs.getPath(internal);
-                }
+                URI rootFs = URI.create(StringUtil.takeUntil(uri.toString(), "!"));
+                String internal = StringUtil.takeAfter(uri.toString(), "!");
+                // keep the file system open.
+                FileSystem zipfs = FileSystems.newFileSystem(rootFs, new HashMap<>());
+                return zipfs.getPath(internal);
             }
         } catch (URISyntaxException | IOException e) {
             throw new RuntimeException(e);
diff --git a/key.util/src/main/java/org/key_project/util/java/StringUtil.java b/key.util/src/main/java/org/key_project/util/java/StringUtil.java
index fccb010cca..c4df641e72 100644
--- a/key.util/src/main/java/org/key_project/util/java/StringUtil.java
+++ b/key.util/src/main/java/org/key_project/util/java/StringUtil.java
@@ -504,14 +504,14 @@ public static String move(@NonNull String text, int line, int charPositionInLine
 
     /// Returns the string until the first match of the given regex.
     public static String takeUntil(String content, String regex) {
-        var array = content.split(regex, 1);
+        var array = content.split(regex, 2);
         return array[0];
     }
 
     /// Returns the string after the first match of the given regex.
     public static String takeAfter(String content, String regex) {
-        var array = content.split(regex, 1);
-        return array[0];
+        var array = content.split(regex, 2);
+        return array[1];
     }