diff --git a/datafusion/spark/src/function/map/utils.rs b/datafusion/spark/src/function/map/utils.rs
index f5fff0c4b4c46..0cf5b45ffd0b7 100644
--- a/datafusion/spark/src/function/map/utils.rs
+++ b/datafusion/spark/src/function/map/utils.rs
@@ -202,17 +202,20 @@ fn map_deduplicate_keys(
                         cur_keys_offset + cur_entry_idx,
                     )?
                     .compacted();
+                    // Enforce Spark's default `spark.sql.mapKeyDedupPolicy=EXCEPTION`.
+                    // Native LAST_WIN support is deferred to a follow-up.
                     if seen_keys.contains(&key) {
-                        // TODO: implement configuration and logic for spark.sql.mapKeyDedupPolicy=EXCEPTION (this is default spark-config)
-                        // exec_err!("invalid argument: duplicate keys in map")
-                        // https://github.com/apache/spark/blob/cf3a34e19dfcf70e2d679217ff1ba21302212472/sql/catalyst/src/main/scala/org/apache/spark/sql/internal/SQLConf.scala#L4961
-                    } else {
-                        // This code implements deduplication logic for spark.sql.mapKeyDedupPolicy=LAST_WIN (this is NOT default spark-config)
-                        keys_mask_one[cur_entry_idx] = true;
-                        values_mask_one[cur_entry_idx] = true;
-                        seen_keys.insert(key);
-                        new_last_offset += 1;
+                        return exec_err!(
+                            "[DUPLICATED_MAP_KEY] Duplicate map key {key} was found, \
+                             please check the input data. If you want to remove the \
+                             duplicated keys, you can set spark.sql.mapKeyDedupPolicy \
+                             to LAST_WIN so that the key inserted at last takes precedence."
+                        );
                     }
+                    keys_mask_one[cur_entry_idx] = true;
+                    values_mask_one[cur_entry_idx] = true;
+                    seen_keys.insert(key);
+                    new_last_offset += 1;
                 }
             }
         } else {
diff --git a/datafusion/sqllogictest/test_files/spark/map/map_from_arrays.slt b/datafusion/sqllogictest/test_files/spark/map/map_from_arrays.slt
index a26b0435c9291..c961f183befd9 100644
--- a/datafusion/sqllogictest/test_files/spark/map/map_from_arrays.slt
+++ b/datafusion/sqllogictest/test_files/spark/map/map_from_arrays.slt
@@ -118,11 +118,9 @@ SELECT
 ----
 {outer_key1: {inner_a: 1, inner_b: 2}, outer_key2: {inner_x: 10, inner_y: 20, inner_z: 30}}
 
-# Test with duplicate keys
-query ?
+# Test with duplicate keys: raises DUPLICATED_MAP_KEY under Spark's default policy
+query error DataFusion error: Execution error: \[DUPLICATED_MAP_KEY\] Duplicate map key true was found
 SELECT map_from_arrays(array(true, false, true), array('a', NULL, 'b'));
-----
-{false: NULL, true: b}
 
 # Tests with different list types
 query ?
diff --git a/datafusion/sqllogictest/test_files/spark/map/map_from_entries.slt b/datafusion/sqllogictest/test_files/spark/map/map_from_entries.slt
index 19b46886a027e..7aec6b3264f4a 100644
--- a/datafusion/sqllogictest/test_files/spark/map/map_from_entries.slt
+++ b/datafusion/sqllogictest/test_files/spark/map/map_from_entries.slt
@@ -151,14 +151,12 @@ SELECT
 ----
 {outer_key1: {inner_a: 1, inner_b: 2}, outer_key2: {inner_x: 10, inner_y: 20, inner_z: 30}}
 
-# Test with duplicate keys
-query ?
+# Test with duplicate keys: raises DUPLICATED_MAP_KEY under Spark's default policy
+query error DataFusion error: Execution error: \[DUPLICATED_MAP_KEY\] Duplicate map key true was found
 SELECT map_from_entries(array(
-    struct(true, 'a'), 
-    struct(false, 'b'), 
+    struct(true, 'a'),
+    struct(false, 'b'),
     struct(true, 'c'),
-    struct(false, cast(NULL as string)), 
+    struct(false, cast(NULL as string)),
     struct(true, 'd')
 ));
-----
-{false: NULL, true: d}