diff --git a/src/matrix-api-types.c b/src/matrix-api-types.c
index f4ae089..78a8164 100644
--- a/src/matrix-api-types.c
+++ b/src/matrix-api-types.c
@@ -38,6 +38,8 @@
  *                               incomplete
  * @MATRIX_API_ERROR_BAD_RESPONSE: malformed response, or the response
  *                                 is not a JSON object
+ * @MATRIX_API_ERROR_INVALID_ROOM_ID: the provided string doesn’t
+ *                                    contain a valid room ID
  * @MATRIX_API_ERROR_MISSING_TOKEN: authorization token is missing
  *                                  from the request
  * @MATRIX_API_ERROR_FORBIDDEN: access was forbidden (e.g. due to a
diff --git a/src/matrix-api-types.h b/src/matrix-api-types.h
index 2e45ba1..8322804 100644
--- a/src/matrix-api-types.h
+++ b/src/matrix-api-types.h
@@ -29,6 +29,7 @@ typedef enum {
     MATRIX_API_ERROR_COMMUNICATION_ERROR,
     MATRIX_API_ERROR_INCOMPLETE,
     MATRIX_API_ERROR_BAD_RESPONSE,
+    MATRIX_API_ERROR_INVALID_ROOM_ID,
 
     /* Add Matrix-defined error codes under here, changing `M_` to
      * `MATRIX_API_ERROR`, i.e. `M_FORBIDDEN` =>
diff --git a/src/matrix-api.c b/src/matrix-api.c
index ef97bbe..eab5054 100644
--- a/src/matrix-api.c
+++ b/src/matrix-api.c
@@ -1025,7 +1025,7 @@ matrix_api_invite_user(MatrixAPI *api,
  *            finished
  * @user_data: (closure): user data to pass to the callback function
  *             @callback
- * @room_id_or_alias: the room ID or room alias to join to
+ * @room_ids: the room ID to join to
  * @error: return location for a #GError, or %NULL
  *
  * Join a room.
@@ -1034,7 +1034,7 @@ void
 matrix_api_join_room(MatrixAPI *api,
                      MatrixAPICallback callback,
                      gpointer user_data,
-                     const gchar *room_id_or_alias,
+                     const gchar *room_id,
                      GError **error)
 {
     g_return_if_fail(MATRIX_IS_API(api));
diff --git a/src/matrix-api.h b/src/matrix-api.h
index 330a986..6e2ae35 100644
--- a/src/matrix-api.h
+++ b/src/matrix-api.h
@@ -222,7 +222,7 @@ struct _MatrixAPIInterface {
     void (*join_room)(MatrixAPI *api,
                       MatrixAPICallback callback,
                       gpointer user_data,
-                      const gchar *room_id_or_alias,
+                      const gchar *room_id,
                       GError **error);
     void (*leave_room)(MatrixAPI *api,
                        MatrixAPICallback callback,
diff --git a/src/matrix-http-api.c b/src/matrix-http-api.c
index b1ed2c4..9efc559 100644
--- a/src/matrix-http-api.c
+++ b/src/matrix-http-api.c
@@ -962,6 +962,35 @@ i_list_public_rooms(MatrixAPI *api,
           error);
 }
 
+static void
+i_join_room(MatrixAPI *api,
+            MatrixAPICallback callback,
+            gpointer user_data,
+            const gchar *room_id,
+            GError **error)
+{
+    gchar *encoded_room_id, *path;
+
+    // TODO: a more thorough check should be used here
+    if (*room_id != '!') {
+        g_set_error(err,
+                    MATRIX_API_ERROR, MATRIX_API_ERROR_INVALID_ROOM_ID,
+                    "Invalid room ID");
+
+        return;
+    }
+
+    encoded_room_id = soup_uri_encode(room_id_or_alias, NULL);
+    path = g_strdup_printf("rooms/%s/join", encoded_room_id);
+    g_free(encoded_room_id);
+
+    _send(MATRIX_HTTP_API(api),
+          callback, user_data,
+          "POST", path, NULL, NULL,
+          error);
+    g_free(path);
+}
+
 static void
 matrix_http_api_matrix_api_init(MatrixAPIInterface *iface)
 {
@@ -977,4 +1006,5 @@ matrix_http_api_matrix_api_init(MatrixAPIInterface *iface)
     iface->event_stream = i_event_stream;
     iface->leave_room = i_leave_room;
     iface->list_public_rooms = i_list_public_rooms;
+    iface->join_room = i_join_room;
 }
diff --git a/src/test-client.c b/src/test-client.c
index cdc6d3e..1269b96 100644
--- a/src/test-client.c
+++ b/src/test-client.c
@@ -58,10 +58,8 @@ create_room_finished(MatrixAPI *api,
         g_printf("Room registered\n");
     }
 
-    matrix_api_initial_sync(MATRIX_API(api),
-                            initial_sync_finished,
-                            data, 10, TRUE,
-                            NULL);
+    matrix_api_join_room(api, NULL, NULL, "#matrix-glib-sdk-test:elxa4y5sd12", NULL);
+    matrix_api_list_public_rooms(api, NULL, NULL, NULL);
 }
 
 static void
@@ -93,8 +91,10 @@ login_finished(MatrixAPI *api, JsonNode *content, gpointer data, GError *err)
 
         g_printf("Logged in as %s\n", user_id);
 
-        matrix_api_list_public_rooms(api, NULL, NULL, NULL);
-
+        matrix_api_initial_sync(MATRIX_API(api),
+                                initial_sync_finished,
+                                data, 10, TRUE,
+                                NULL);
         matrix_api_create_room(api,
                                create_room_finished, NULL,
                                MATRIX_API_ROOM_PRESET_PUBLIC,