diff --git a/examples/capi.c b/examples/capi.c
index 1be88d2..92f05a3 100644
--- a/examples/capi.c
+++ b/examples/capi.c
@@ -42,13 +42,12 @@ static void query(union evm_variant* result,
     }
 }
 
-static void update(struct evm_env* env,
-                   enum evm_update_key key,
-                   const struct evm_uint160be* addr,
-                   const union evm_variant* arg1,
-                   const union evm_variant* arg2)
+static void set_storage(struct evm_env* env,
+                        const struct evm_uint160be* addr,
+                        const struct evm_uint256be* key,
+                        const struct evm_uint256be* value)
 {
-    printf("EVM-C: UPDATE %d\n", key);
+    printf("EVM-C: SSTORE");
 }
 
 static void call(struct evm_result* result,
@@ -76,7 +75,7 @@ int main(int argc, char *argv[]) {
     if (factory.abi_version != EVM_ABI_VERSION)
         return 1;  // Incompatible ABI version.
 
-    struct evm_instance* jit = factory.create(query, update, NULL, call,
+    struct evm_instance* jit = factory.create(query, set_storage, NULL, call,
                                               get_tx_context, get_block_hash,
                                               NULL);
 
diff --git a/examples/examplevm.c b/examples/examplevm.c
index c0b3d25..2be14d8 100644
--- a/examples/examplevm.c
+++ b/examples/examplevm.c
@@ -8,7 +8,7 @@ struct examplevm
 {
     struct evm_instance instance;
     evm_query_state_fn query_fn;
-    evm_update_state_fn update_fn;
+    evm_set_storage_fn set_storage_fn;
     evm_call_fn call_fn;
     evm_get_tx_context_fn get_tx_context_fn;
     evm_get_block_hash_fn get_block_hash_fn;
@@ -102,9 +102,7 @@ static struct evm_result execute(struct evm_instance* instance,
         const struct evm_uint256be index = {{0,}};
         vm->query_fn(&value, env, EVM_SLOAD, &msg->address, &index);
         value.uint256be.bytes[31] += 1;
-        union evm_variant arg;
-        arg.uint256be = index;
-        vm->update_fn(env, EVM_SSTORE, &msg->address, &arg, &value);
+        vm->set_storage_fn(env, &msg->address, &index, &value.uint256be);
         ret.code = EVM_SUCCESS;
         return ret;
     }
@@ -117,7 +115,7 @@ static struct evm_result execute(struct evm_instance* instance,
 }
 
 static struct evm_instance* evm_create(evm_query_state_fn query_fn,
-                                       evm_update_state_fn update_fn,
+                                       evm_set_storage_fn update_fn,
                                        evm_selfdestruct_fn selfdestruct_fn,
                                        evm_call_fn call_fn,
                                        evm_get_tx_context_fn get_tx_context_fn,
@@ -130,7 +128,7 @@ static struct evm_instance* evm_create(evm_query_state_fn query_fn,
     interface->execute = execute;
     interface->set_option = evm_set_option;
     vm->query_fn = query_fn;
-    vm->update_fn = update_fn;
+    vm->set_storage_fn = update_fn;
     vm->call_fn = call_fn;
     vm->get_tx_context_fn = get_tx_context_fn;
     vm->get_block_hash_fn = get_block_hash_fn;
diff --git a/include/evm.h b/include/evm.h
index 4d5e496..01aa057 100644
--- a/include/evm.h
+++ b/include/evm.h
@@ -270,30 +270,19 @@ typedef void (*evm_query_state_fn)(union evm_variant* result,
                                    const struct evm_uint160be* address,
                                    const struct evm_uint256be* storage_key);
 
-/// The update callback key.
-enum evm_update_key {
-    EVM_SSTORE = 0,        ///< Update storage entry
-};
-
-
-/// Update callback function.
+/// Set storage callback function.
 ///
-/// This callback function is used by the EVM to modify contract state in the
-/// host application.
-/// @param env  Pointer to execution environment managed by the host
-///             application.
-/// @param key  The kind of the update. See evm_update_key and details below.
-///
-/// ## Kinds of updates
-///
-/// - ::EVM_SSTORE
-///   @param arg1 evm_variant::uint256be  The index of the storage entry.
-///   @param arg2 evm_variant::uint256be  The value to be stored.
-typedef void (*evm_update_state_fn)(struct evm_env* env,
-                                    enum evm_update_key key,
-                                    const struct evm_uint160be* address,
-                                    const union evm_variant* arg1,
-                                    const union evm_variant* arg2);
+/// This callback function is used by an EVM to update the given contract
+/// storage entry
+/// @param env      Pointer to execution environment managed by the host
+///                 application.
+/// @param address  The address of the contract.
+/// @param key      The index of the storage entry.
+/// @param value    The value to be stored.
+typedef void (*evm_set_storage_fn)(struct evm_env* env,
+                                   const struct evm_uint160be* address,
+                                   const struct evm_uint256be* key,
+                                   const struct evm_uint256be* value);
 
 /// Selfdestruct callback function.
 ///
@@ -351,7 +340,7 @@ struct evm_instance;  ///< Forward declaration.
 /// @param get_block_hash_fn  Pointer to get block hash function. Nonnull.
 /// @return           Pointer to the created EVM instance.
 typedef struct evm_instance* (*evm_create_fn)(evm_query_state_fn query_fn,
-                                              evm_update_state_fn update_fn,
+                                              evm_set_storage_fn update_fn,
                                               evm_selfdestruct_fn selfdestruct_fn,
                                               evm_call_fn call_fn,
                                               evm_get_tx_context_fn get_tx_context_fn,