diff --git a/x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/EsqlFunctionRegistry.java b/x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/EsqlFunctionRegistry.java
index d5dcc26942571..8ee97ca80a361 100644
--- a/x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/EsqlFunctionRegistry.java
+++ b/x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/EsqlFunctionRegistry.java
@@ -438,6 +438,11 @@ public static String normalizeName(String name) {
     }
 
     public record ArgSignature(String name, String[] type, String description, boolean optional, DataType targetDataType) {
+
+        public ArgSignature(String name, String[] type, String description, boolean optional) {
+            this(name, type, description, optional, UNSUPPORTED);
+        }
+
         @Override
         public String toString() {
             return "ArgSignature{"
@@ -481,13 +486,13 @@ public List<String> argDescriptions() {
     /**
      * Build a list target data types, which is used by ImplicitCasting to convert string literals to a target data type.
      */
-    public static DataType getTargetType(String[] names) {
+    private static DataType getTargetType(String[] names) {
         List<DataType> types = new ArrayList<>();
         for (String name : names) {
             DataType type = DataType.fromTypeName(name);
             if (type != null && type != UNSUPPORTED) { // A type should not be null or UNSUPPORTED, just a sanity check here
                 // If the function takes strings as input, there is no need to cast a string literal to it.
-                // Return UNSUPPORTED, so that ImplicitCasting doesn't process it.
+                // Return UNSUPPORTED means that ImplicitCasting doesn't support this argument, and it will be skipped by ImplicitCasting.
                 if (isString(type)) {
                     return UNSUPPORTED;
                 }
diff --git a/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/AbstractFunctionTestCase.java b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/AbstractFunctionTestCase.java
index 6a552f400d36e..181b8d52bf888 100644
--- a/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/AbstractFunctionTestCase.java
+++ b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/AbstractFunctionTestCase.java
@@ -879,8 +879,7 @@ public static void renderDocs() throws IOException {
                     "elseValue",
                     trueValue.type(),
                     "The value that's returned when no condition evaluates to `true`.",
-                    true,
-                    EsqlFunctionRegistry.getTargetType(trueValue.type())
+                    true
                 );
                 description = new EsqlFunctionRegistry.FunctionDescription(
                     description.name(),
@@ -1085,8 +1084,7 @@ private static void renderDocsForOperators(String name) throws IOException {
                 String[] type = paramInfo == null ? new String[] { "?" } : paramInfo.type();
                 String desc = paramInfo == null ? "" : paramInfo.description().replace('\n', ' ');
                 boolean optional = paramInfo == null ? false : paramInfo.optional();
-                DataType targetDataType = EsqlFunctionRegistry.getTargetType(type);
-                args.add(new EsqlFunctionRegistry.ArgSignature(paramName, type, desc, optional, targetDataType));
+                args.add(new EsqlFunctionRegistry.ArgSignature(paramName, type, desc, optional));
             }
         }
         renderKibanaFunctionDefinition(name, functionInfo, args, likeOrInOperator(name));