diff --git a/RELEASENOTE.md b/RELEASENOTE.md
index e31e9d4cf..afe8e0395 100644
--- a/RELEASENOTE.md
+++ b/RELEASENOTE.md
@@ -1,6 +1,10 @@
 Selenese Runner Java Relase Note
 ================================
 
+### 3.33.0
+
+* Fix not to replace undefined variables. (#324)
+
 ### 3.32.0
 
 * Change not to retry the composite command if an error occurs. (#320)
diff --git a/src/main/java/jp/vmi/selenium/selenese/VarsMap.java b/src/main/java/jp/vmi/selenium/selenese/VarsMap.java
index ac1ba8803..55b55299c 100644
--- a/src/main/java/jp/vmi/selenium/selenese/VarsMap.java
+++ b/src/main/java/jp/vmi/selenium/selenese/VarsMap.java
@@ -98,11 +98,15 @@ public String replaceVars(boolean isScript, String expr) {
             if (prevEnd < nextStart)
                 result.append(expr.substring(prevEnd, nextStart));
             String name = matcher.group("name");
-            Object rawValue = get(name);
-            if (isScript)
-                result.append(new Gson().toJson(rawValue));
-            else
-                result.append(SeleniumUtils.convertToString(rawValue));
+            if (containsKey(name)) {
+                Object rawValue = get(name);
+                if (isScript)
+                    result.append(new Gson().toJson(rawValue));
+                else
+                    result.append(SeleniumUtils.convertToString(rawValue));
+            } else {
+                result.append(matcher.group());
+            }
             prevEnd = matcher.end();
         }
         if (prevEnd < expr.length())
diff --git a/src/test/java/jp/vmi/selenium/selenese/DriverDependentTest.java b/src/test/java/jp/vmi/selenium/selenese/DriverDependentTest.java
index f1ca8763b..36dcfba97 100644
--- a/src/test/java/jp/vmi/selenium/selenese/DriverDependentTest.java
+++ b/src/test/java/jp/vmi/selenium/selenese/DriverDependentTest.java
@@ -501,4 +501,12 @@ public void testNoReplaceAlertMethod() {
 
         runner.setReplaceAlertMethod(true);
     }
+
+    @Test
+    public void issue324() {
+        assumeNot(PHANTOMJS, HTMLUNIT, IE);
+        execute("testcase_issue324.side");
+        assertThat(result, is(instanceOf(Success.class)));
+    }
+
 }
diff --git a/src/test/resources/selenese/testcase_issue324.side b/src/test/resources/selenese/testcase_issue324.side
new file mode 100644
index 000000000..730a42418
--- /dev/null
+++ b/src/test/resources/selenese/testcase_issue324.side
@@ -0,0 +1,56 @@
+{
+  "id": "e55b5d28-ec31-4401-8d2a-5b7829f36d82",
+  "version": "2.0",
+  "name": "test",
+  "url": "http://localhost/",
+  "tests": [{
+    "id": "834b529f-c7fc-4d43-bbdf-0cfabe285c75",
+    "name": "issue324",
+    "commands": [{
+      "id": "839bb8c7-14da-49dd-9554-e593be46fd3e",
+      "comment": "",
+      "command": "open",
+      "target": "http://localhost/",
+      "targets": [],
+      "value": ""
+    }, {
+      "id": "392e5b60-ed91-445b-9827-001d5695fece",
+      "comment": "",
+      "command": "store",
+      "target": "hello",
+      "targets": [],
+      "value": "var_side01"
+    }, {
+      "id": "2cdd69da-89eb-4c45-9265-3f4497c8d632",
+      "comment": "",
+      "command": "executeScript",
+      "target": "const var_js = ${var_side01}; return `${var_js} world`;",
+      "targets": [],
+      "value": "var_side02"
+    }, {
+      "id": "7c5e78e4-f6fd-4a21-8e0b-c8a29633abeb",
+      "comment": "",
+      "command": "echo",
+      "target": "var_side01=${var_side01}, var_side02=${var_side02}",
+      "targets": [],
+      "value": ""
+    }, {
+      "id": "846d5221-9f82-48f3-8b65-5711614b163f",
+      "comment": "",
+      "command": "assert",
+      "target": "var_side02",
+      "targets": [],
+      "value": "hello world"
+    }]
+  }],
+  "suites": [{
+    "id": "e7b7100f-dcc5-4d14-a6cc-7987a9d6f804",
+    "name": "Default Suite",
+    "persistSession": false,
+    "parallel": false,
+    "timeout": 300,
+    "tests": ["834b529f-c7fc-4d43-bbdf-0cfabe285c75"]
+  }],
+  "urls": ["http://localhost/"],
+  "plugins": []
+}
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