diff --git a/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoRules.java b/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoRules.java
index 00c14f1c683b..bae5ace361bc 100644
--- a/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoRules.java
+++ b/mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoRules.java
@@ -103,9 +103,6 @@ static List<String> mongoFieldNames(final RelDataType rowType) {
   }
 
   static String maybeQuote(String s) {
-    if (!needsQuote(s)) {
-      return s;
-    }
     return quote(s);
   }
 
@@ -113,21 +110,6 @@ static String quote(String s) {
     return "'" + s + "'"; // TODO: handle embedded quotes
   }
 
-  private static boolean needsQuote(String s) {
-    if (!s.isEmpty()
-        && (!Character.isJavaIdentifierStart(s.charAt(0)) || s.charAt(0) == '$')) {
-      return true;
-    }
-
-    for (int i = 1, n = s.length(); i < n; i++) {
-      char c = s.charAt(i);
-      if (!Character.isJavaIdentifierPart(c)) {
-        return true;
-      }
-    }
-    return false;
-  }
-
   /** Translator from {@link RexNode} to strings in MongoDB's expression
    * language. */
   static class RexToMongoTranslator extends RexVisitorImpl<String> {