diff --git a/src/sci/impl/evaluator.cljc b/src/sci/impl/evaluator.cljc
index f51389f8..d694ca14 100644
--- a/src/sci/impl/evaluator.cljc
+++ b/src/sci/impl/evaluator.cljc
@@ -140,31 +140,40 @@
     (if-not (identical? none-sentinel v)
       v
       (let [instance-class #?(:clj (or (when tag-class
-                                          (if (instance? tag-class instance-expr*)
-                                            tag-class
-                                            (class instance-expr*)))
-                                        (class instance-expr*))
+                                         (if (instance? tag-class instance-expr*)
+                                           tag-class
+                                           (class instance-expr*)))
+                                       (class instance-expr*))
                               :cljs (type instance-expr*))
             env @(:env ctx)
             class->opts (:class->opts env)
             allowed? (or
                       #?(:cljs allowed)
-                      (get class->opts :allow)
-                      (let [instance-class-name #?(:clj (.getName ^Class instance-class)
-                                                   :cljs (.-name instance-class))
-                            instance-class-symbol (symbol instance-class-name)]
-                        (get class->opts instance-class-symbol)))
-            ^Class target-class (if allowed? instance-class
-                                    (when-let [f (:public-class env)]
-                                      (f instance-expr*)))]
-        ;; we have to check options at run time, since we don't know what the class
-        ;; of instance-expr is at analysis time
-        (when-not #?(:clj target-class
-                     :cljs allowed?)
-          (throw-error-with-location (str "Method " method-str " on " instance-class " not allowed!") instance-expr))
-        (if field-access
-          (interop/invoke-instance-field instance-expr* target-class method-str)
-          (interop/invoke-instance-method ctx bindings instance-expr* target-class method-str args arg-count arg-types))))))
+                      (get class->opts :allow))]
+        (if allowed?
+          (if field-access
+            (interop/invoke-instance-field instance-expr* instance-class method-str)
+            (interop/invoke-instance-method ctx bindings instance-expr* instance-class method-str args arg-count arg-types))
+          (let [instance-class-name #?(:clj (.getName ^Class instance-class)
+                                       :cljs (.-name instance-class))
+                instance-class-symbol (symbol instance-class-name)]
+            (if-let [class-config (get class->opts instance-class-symbol)]
+              (if-let [f (some-> class-config :instance-methods
+                                 (get (symbol method-str)))]
+                (apply f instance-expr* (map (fn [arg] (sci.impl.types/eval arg ctx bindings)) args))
+                (if field-access
+                  (interop/invoke-instance-field instance-expr* instance-class method-str)
+                  (interop/invoke-instance-method ctx bindings instance-expr* instance-class method-str args arg-count arg-types)))
+              (let [^Class target-class (when-let [f (:public-class env)]
+                                          (f instance-expr*))]
+
+                ;; we have to check options at run time, since we don't know what the class
+                ;; of instance-expr is at analysis time
+                (if target-class
+                  (if field-access
+                    (interop/invoke-instance-field instance-expr* target-class method-str)
+                    (interop/invoke-instance-method ctx bindings instance-expr* target-class method-str args arg-count arg-types))
+                  (throw-error-with-location (str "Method " method-str " on " instance-class " not allowed!") instance-expr))))))))))
 
 ;;;; End interop
 
diff --git a/test/sci/interop_test.cljc b/test/sci/interop_test.cljc
index c41701de..af5d797b 100644
--- a/test/sci/interop_test.cljc
+++ b/test/sci/interop_test.cljc
@@ -42,7 +42,19 @@
          (is (= #{:a} (tu/eval* "(.keySet {:a 1})"
                                 {:classes {'java.util.Map 'java.util.Map
                                            :public-class (fn [o]
-                                                           (when (instance? java.util.Map o) java.util.Map))}})))))))
+                                                           (when (instance? java.util.Map o) java.util.Map))}})))))
+     (testing "single method override"
+       (let [config {:classes {'java.lang.String
+                               {:class java.lang.String
+                                :instance-methods {'lastIndexOf (fn [s needle] (.lastIndexOf s needle)) ; String/.lastIndexOf syntax only added as of 1.12
+                                                   'toString
+                                                   ;; REVIEW should toString also receive the class like the functions in :static-methods
+                                                   (fn [_s]
+                                                     :dude)}}}}]
+         (is (= :dude (sci/eval-string "(.toString \"your name\")" config)))
+         (is (= 9 (sci/eval-string "(.length \"your name\")" config)))
+         (is (= 5 (sci/eval-string "(let [needle \"name\"] (.lastIndexOf \"your name\" needle))" config)))))))  
+
 
 #?(:clj
    (deftest instance-fields