diff --git a/tox.ini b/tox.ini
index abf21c4f..298ad013 100644
--- a/tox.ini
+++ b/tox.ini
@@ -5,7 +5,7 @@ envlist=py{35,36,37,py3}-marshmallow{2,3}, cython-marshmallow{2,3}
 deps=
     -rrequirements/build_common.txt
     marshmallow2: marshmallow <3.0
-    marshmallow3: marshmallow==3.0.0rc6
+    marshmallow3: marshmallow >=3.0.0rc5
 
 whitelist_externals=flake8
 commands=py.test --cov-report html --cov hug -n auto tests
@@ -13,7 +13,7 @@ commands=py.test --cov-report html --cov hug -n auto tests
 [testenv:py37-black]
 deps=
     -rrequirements/build_style_tools.txt
-    marshmallow==3.0.0rc6
+    marshmallow >=3.0.0rc5
 
 whitelist_externals=flake8
 commands=black --check --verbose -l 100 hug
@@ -21,7 +21,7 @@ commands=black --check --verbose -l 100 hug
 [testenv:py37-vulture]
 deps=
     -rrequirements/build_style_tools.txt
-    marshmallow==3.0.0rc6
+    marshmallow >=3.0.0rc5
 
 whitelist_externals=flake8
 commands=vulture hug --min-confidence 100 --ignore-names req_succeeded
@@ -30,7 +30,7 @@ commands=vulture hug --min-confidence 100 --ignore-names req_succeeded
 [testenv:py37-flake8]
 deps=
     -rrequirements/build_style_tools.txt
-    marshmallow==3.0.0rc6
+    marshmallow >=3.0.0rc5
 
 whitelist_externals=flake8
 commands=flake8 hug
@@ -38,7 +38,7 @@ commands=flake8 hug
 [testenv:py37-bandit]
 deps=
     -rrequirements/build_style_tools.txt
-    marshmallow==3.0.0rc6
+    marshmallow >=3.0.0rc5
 
 whitelist_externals=flake8
 commands=bandit -r hug/ -ll
@@ -46,7 +46,7 @@ commands=bandit -r hug/ -ll
 [testenv:py37-isort]
 deps=
     -rrequirements/build_style_tools.txt
-    marshmallow==3.0.0rc6
+    marshmallow >=3.0.0rc5
 
 whitelist_externals=flake8
 commands=isort -c --diff --recursive hug