diff --git a/vaadin-testbench-loadtest/testbench-converter-plugin/src/main/java/com/vaadin/testbench/loadtest/util/K6TestRefactorer.java b/vaadin-testbench-loadtest/testbench-converter-plugin/src/main/java/com/vaadin/testbench/loadtest/util/K6TestRefactorer.java
index e0ad261dc..59a743c17 100644
--- a/vaadin-testbench-loadtest/testbench-converter-plugin/src/main/java/com/vaadin/testbench/loadtest/util/K6TestRefactorer.java
+++ b/vaadin-testbench-loadtest/testbench-converter-plugin/src/main/java/com/vaadin/testbench/loadtest/util/K6TestRefactorer.java
@@ -499,9 +499,9 @@ private List<RequestInfo> parseRequestsWithTiming(List<String> lines) {
             }
 
             if (inRequest) {
-                int opens = countOccurrences(line, '(');
+                int opens = countUnquotedOccurrences(line, '(');
                 parenCount += opens;
-                parenCount -= countOccurrences(line, ')');
+                parenCount -= countUnquotedOccurrences(line, ')');
                 if (opens > 0) {
                     seenOpenParen = true;
                 }
@@ -647,8 +647,8 @@ private String insertJsessionExtraction(String content) {
             }
 
             if (inFirstAppRequest) {
-                braceCount += countOccurrences(line, '{');
-                braceCount -= countOccurrences(line, '}');
+                braceCount += countUnquotedOccurrences(line, '{');
+                braceCount -= countUnquotedOccurrences(line, '}');
 
                 if (braceCount == 0 && line.contains(")")) {
                     insertLineIndex = i;
@@ -687,8 +687,8 @@ private String insertVaadinExtraction(String content) {
             }
 
             if (inInitRequest) {
-                braceCount += countOccurrences(line, '{');
-                braceCount -= countOccurrences(line, '}');
+                braceCount += countUnquotedOccurrences(line, '{');
+                braceCount -= countUnquotedOccurrences(line, '}');
 
                 if (braceCount == 0 && line.contains(")")) {
                     insertLineIndex = i;
@@ -705,10 +705,35 @@ private String insertVaadinExtraction(String content) {
         return content;
     }
 
-    private int countOccurrences(String str, char c) {
+    /**
+     * Counts occurrences of {@code target} in {@code str}, ignoring any
+     * occurrences that fall inside a JavaScript string literal delimited by
+     * {@code '}, {@code "}, or {@code `}. Backslash escapes inside strings are
+     * honored. This is what keeps a {@code )} inside a header value like
+     * {@code 'sec-ch-ua': '"Not/A)Brand";v="99"'} from being mistaken for the
+     * closing paren of an {@code http.get(...)} call.
+     * <p>
+     * The scan is per-line: {@link HarToK6Converter} escapes
+     * {@code \n}/{@code \r}/ {@code \t} in URLs, headers, and bodies, so
+     * generated string literals never span multiple lines. Template-literal
+     * interpolations ({@code ${...}}) are treated as opaque string content —
+     * the converter only emits interpolations of bare identifiers, none of
+     * which contain {@code (}, {@code )}, {@code {}, or {@code }}.
+     */
+    private int countUnquotedOccurrences(String str, char target) {
         int count = 0;
+        char stringDelim = 0;
         for (int i = 0; i < str.length(); i++) {
-            if (str.charAt(i) == c) {
+            char c = str.charAt(i);
+            if (stringDelim != 0) {
+                if (c == '\\' && i + 1 < str.length()) {
+                    i++;
+                } else if (c == stringDelim) {
+                    stringDelim = 0;
+                }
+            } else if (c == '\'' || c == '"' || c == '`') {
+                stringDelim = c;
+            } else if (c == target) {
                 count++;
             }
         }
diff --git a/vaadin-testbench-loadtest/testbench-converter-plugin/src/test/java/com/vaadin/testbench/loadtest/util/K6TestRefactorerTest.java b/vaadin-testbench-loadtest/testbench-converter-plugin/src/test/java/com/vaadin/testbench/loadtest/util/K6TestRefactorerTest.java
index 82a4edee1..f81ff7a7d 100644
--- a/vaadin-testbench-loadtest/testbench-converter-plugin/src/test/java/com/vaadin/testbench/loadtest/util/K6TestRefactorerTest.java
+++ b/vaadin-testbench-loadtest/testbench-converter-plugin/src/test/java/com/vaadin/testbench/loadtest/util/K6TestRefactorerTest.java
@@ -144,6 +144,64 @@ export default function() {
                         + refactored);
     }
 
+    @Test
+    void refactorContent_thinkTimesEnabled_headerValueContainsCloseParen_sleepIsNotInjectedInsideHeaders() {
+        K6TestRefactorer refactorer = new K6TestRefactorer(
+                ThinkTimeConfig.DEFAULT);
+
+        // Reproduces the combineScenarios=true breakage: the Chrome sec-ch-ua
+        // header value contains a literal `)` inside a single-quoted JS
+        // string. A non-string-aware paren counter dropped to zero mid-headers
+        // and the sleep() got injected inside the headers object, producing
+        // "Unexpected number" parse errors in k6.
+        String script = """
+                import http from 'k6/http'
+                import { sleep } from 'k6'
+                export default function() {
+                  // HAR_DELTA_MS: 0
+                  // Request 1: GET http://localhost:8080/?v-r=init
+                  let response = http.get(
+                    'http://localhost:8080/?v-r=init',
+                    {
+                      headers: {
+                        'sec-ch-ua': '"Chromium";v="148", "Not/A)Brand";v="99"',
+                        'User-Agent': 'Mozilla/5.0'
+                      },
+                      tags: { name: 'init' }
+                    }
+                  )
+                  // HAR_DELTA_MS: 200
+                  // Request 2: POST http://localhost:8080/?v-r=uidl
+                  response = http.post('http://localhost:8080/?v-r=uidl', '{"event":"click"}')
+                }
+                """;
+
+        String refactored = refactorer.refactorContent(script);
+
+        // A sleep() call should be emitted (page-read delay at the init
+        // block boundary).
+        assertTrue(refactored.contains("sleep("),
+                "Expected at least one sleep() call in refactored output:\n"
+                        + refactored);
+
+        // The `Not/A)Brand` sec-ch-ua line is the bug trigger. After
+        // refactoring it must still be immediately followed by the next
+        // header property — not by a // Think time comment or a sleep()
+        // call, which would mean the sleep was injected inside the
+        // headers object.
+        String triggerLine = "'sec-ch-ua': '\"Chromium\";v=\"148\", \"Not/A)Brand\";v=\"99\"',";
+        int triggerIdx = refactored.indexOf(triggerLine);
+        assertTrue(triggerIdx >= 0,
+                "Expected sec-ch-ua header line to survive refactoring intact:\n"
+                        + refactored);
+        String afterTrigger = refactored
+                .substring(triggerIdx + triggerLine.length()).stripLeading();
+        assertTrue(afterTrigger.startsWith("'User-Agent'"),
+                "sec-ch-ua header was not followed by the User-Agent header — "
+                        + "a sleep() was likely injected inside the headers object:\n"
+                        + refactored);
+    }
+
     @Test
     void refactor_readsInputAndWritesOutputFile() throws IOException {
         Path input = tempDir.resolve("in.js");