diff --git a/paimon-api/src/main/java/org/apache/paimon/rest/auth/DLFOpenApiV4Signer.java b/paimon-api/src/main/java/org/apache/paimon/rest/auth/DLFOpenApiV4Signer.java
index 4c090c7a8b09..1b7e833210ba 100644
--- a/paimon-api/src/main/java/org/apache/paimon/rest/auth/DLFOpenApiV4Signer.java
+++ b/paimon-api/src/main/java/org/apache/paimon/rest/auth/DLFOpenApiV4Signer.java
@@ -34,6 +34,7 @@
 import java.util.Arrays;
 import java.util.HashMap;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.UUID;
 
@@ -252,7 +253,7 @@ private static CanonicalHeadersResult buildCanonicalHeaders(Map<String, String>
         Map<String, String> valueMap = new HashMap<>();
 
         for (Map.Entry<String, String> entry : headers.entrySet()) {
-            String lowerKey = entry.getKey().toLowerCase();
+            String lowerKey = entry.getKey().toLowerCase(Locale.ROOT);
             if (lowerKey.startsWith("x-acs-")
                     || lowerKey.equals(HOST_HEADER)
                     || lowerKey.equals(CONTENT_TYPE_HEADER)) {
diff --git a/paimon-api/src/test/java/org/apache/paimon/rest/auth/DLFOpenApiV4SignerTest.java b/paimon-api/src/test/java/org/apache/paimon/rest/auth/DLFOpenApiV4SignerTest.java
index a81358aa8811..67d40499de78 100644
--- a/paimon-api/src/test/java/org/apache/paimon/rest/auth/DLFOpenApiV4SignerTest.java
+++ b/paimon-api/src/test/java/org/apache/paimon/rest/auth/DLFOpenApiV4SignerTest.java
@@ -25,6 +25,7 @@
 import java.time.ZonedDateTime;
 import java.util.HashMap;
 import java.util.LinkedHashMap;
+import java.util.Locale;
 import java.util.Map;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
@@ -164,6 +165,27 @@ public void testDeterministicSignature() throws Exception {
         assertEquals(auth1, auth2);
     }
 
+    @Test
+    public void testAuthorizationWithTurkishLocale() throws Exception {
+        Locale originalLocale = Locale.getDefault();
+        try {
+            Locale.setDefault(Locale.US);
+            DLFOpenApiV4Signer signer = new DLFOpenApiV4Signer(REGION);
+            DLFToken token = new DLFToken("TestAKId", "TestAKSecret", null, null);
+            RESTAuthParameter restAuthParameter =
+                    new RESTAuthParameter("/test/path", new HashMap<>(), "GET", null);
+            Map<String, String> headers = signer.signHeaders(null, NOW, null, HOST);
+            headers.put("x-acs-signature-nonce", "fixed-nonce-for-test");
+            headers.put("X-ACS-SIGNATURE-NONCE", headers.remove("x-acs-signature-nonce"));
+
+            String expected = signer.authorization(restAuthParameter, token, HOST, headers);
+            Locale.setDefault(new Locale("tr", "TR"));
+            assertEquals(expected, signer.authorization(restAuthParameter, token, HOST, headers));
+        } finally {
+            Locale.setDefault(originalLocale);
+        }
+    }
+
     @Test
     public void testSignatureCoversQueryParameters() throws Exception {
         DLFOpenApiV4Signer signer = new DLFOpenApiV4Signer(REGION);