diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8b1ffbd..41101fb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,7 @@
   * Support much richer range of syntax on `CREATE`/`DROP` statements in general, including columns, `TABLESPACE`, `CASCADE`, `WITH [NO] DATA`, etc.
   * Fix #306 by supporting `CREATE TABLE .. AS ..`.
   * Fix #305 by supporting more complex join clauses.
+  * Fix #303 by supporting MySQL's `ON DUPLICATE KEY UPDATE`.
   * Fix #301 by adding support for `CREATE`/`DROP`/`REFRESH` on `MATERIALIZED VIEW`.
   * Add tests to confirm #299 does not affect v2.
   * Confirm the whole of the [nilenso/honeysql-postgres](https://github.com/nilenso/honeysql-postgres) is implemented out-of-the-box (#293).
diff --git a/doc/clause-reference.md b/doc/clause-reference.md
index 4cb1a7a..0459e21 100644
--- a/doc/clause-reference.md
+++ b/doc/clause-reference.md
@@ -715,6 +715,10 @@ user=> (sql/format {:insert-into :companies
 ["INSERT INTO companies (name) VALUES (?) ON CONFLICT ON CONSTRAINT name_idx DO NOTHING" "Microsoft"]
 ```
 
+## on-duplicate-key-update
+
+This is the MySQL equivalent of `on-update-set` described above.
+
 ## returning
 
 `:returning` accepts a single sequence argument that lists
diff --git a/src/honey/sql.cljc b/src/honey/sql.cljc
index 5eeb92d..b7f29d7 100644
--- a/src/honey/sql.cljc
+++ b/src/honey/sql.cljc
@@ -54,7 +54,7 @@
    :where :group-by :having
    :window :partition-by
    :order-by :limit :offset :for :values
-   :on-conflict :on-constraint :do-nothing :do-update-set
+   :on-conflict :on-constraint :do-nothing :do-update-set :on-duplicate-key-update
    :returning
    :with-data])
 
@@ -754,6 +754,8 @@
          :on-constraint   #'format-selector
          :do-nothing      (fn [k _] (vector (sql-kw k)))
          :do-update-set   #'format-do-update-set
+         ;; MySQL-specific but might as well be always enabled:
+         :on-duplicate-key-update #'format-do-update-set
          :returning       #'format-selects
          :with-data       #'format-with-data}))
 
diff --git a/src/honey/sql/helpers.cljc b/src/honey/sql/helpers.cljc
index 222ab61..844c619 100644
--- a/src/honey/sql/helpers.cljc
+++ b/src/honey/sql/helpers.cljc
@@ -569,6 +569,10 @@
   [& args]
   (generic :do-update-set args))
 
+(defn on-duplicate-key-update
+  [& args]
+  (generic :on-duplicate-key-update args))
+
 (defn returning
   "Accepts any number of column names to return from an
   insert operation:
diff --git a/test/honey/sql/helpers_test.cljc b/test/honey/sql/helpers_test.cljc
index 686e8cf..c894d08 100644
--- a/test/honey/sql/helpers_test.cljc
+++ b/test/honey/sql/helpers_test.cljc
@@ -10,8 +10,9 @@
                      create-materialized-view drop-view drop-materialized-view
                      cross-join do-update-set drop-column drop-index drop-table from full-join
                      group-by having insert-into
-                     join-by join left-join limit offset on-conflict order-by
-                     over partition-by refresh-materialized-view
+                     join-by join left-join limit offset on-conflict
+                     on-duplicate-key-update
+                     order-by over partition-by refresh-materialized-view
                      rename-column rename-table returning right-join
                      select select-distinct values where window with with-columns
                      with-data]]))
@@ -649,3 +650,24 @@
                  (f {k [:and [:a] [:b]]}
                     :or
                     [:x] [:y]))))))))
+
+(deftest mysql-on-duplicate-key-update
+  (testing "From https://www.mysqltutorial.org/mysql-insert-or-update-on-duplicate-key-update"
+    (is (= (sql/format (-> (insert-into :device)
+                           (columns :name)
+                           (values [["Printer"]])
+                           (on-duplicate-key-update {:name "Printer"})))
+           ["INSERT INTO device (name) VALUES (?) ON DUPLICATE KEY UPDATE name = ?"
+            "Printer" "Printer"]))
+    (is (= (sql/format (-> (insert-into :device)
+                           (columns :id :name)
+                           (values [[4 "Printer"]])
+                           (on-duplicate-key-update {:name "Central Printer"})))
+           ["INSERT INTO device (id, name) VALUES (?, ?) ON DUPLICATE KEY UPDATE name = ?"
+            4 "Printer" "Central Printer"]))
+    (is (= (sql/format (-> (insert-into :table)
+                           (columns :c1)
+                           (values [[42]])
+                           (on-duplicate-key-update {:c1 [:+ [:values :c1] 1]})))
+           ["INSERT INTO table (c1) VALUES (?) ON DUPLICATE KEY UPDATE c1 = VALUES(c1) + ?"
+            42 1]))))
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