diff --git a/.travis.yml b/.travis.yml
index 0886088..657d91e 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -14,14 +14,14 @@ matrix:
     - python: "3.6"
     - python: "3.7"
     - python: "3.8"
-    - python: "3.9-dev"
-    - python: "3.8"
+    - python: "3.9"
+    - python: "3.9"
       env: TOXENV=flake8
 
 install:
   - pip install -U pip wheel
   - pip install -U Cython
-  - pip install -U tox-travis tox poetry==1.1.0
+  - pip install -U tox-travis tox poetry==1.1.6
 
 script:
   - tox
diff --git a/pyproject.toml b/pyproject.toml
index bc2897a..02ce4c0 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "flatten-dict"
-version = "0.3.0"
+version = "0.4.0"
 description = "A flexible utility for flattening and unflattening dict-like objects in Python."
 authors = ["Ian Lin <you@example.com>"]
 license = "MIT"