diff --git a/requirements.txt b/requirements.txt
index 3acfae6..610fd3e 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,2 +1,2 @@
-oscrypto
+oscrypto==0.16.0
 six
diff --git a/setup.py b/setup.py
index 4167166..c664cf8 100755
--- a/setup.py
+++ b/setup.py
@@ -25,7 +25,7 @@
     ],
     tests_require=[
         "mock",
-        "oscrypto",
+        "oscrypto==0.16.0",
         "six"
     ],
     classifiers=[
diff --git a/src/validatesns/__init__.py b/src/validatesns/__init__.py
index 4fb1640..d44194a 100644
--- a/src/validatesns/__init__.py
+++ b/src/validatesns/__init__.py
@@ -155,7 +155,7 @@ def _validate_signature(self, signature, content):
             certificate = certificate.encode()
 
         if isinstance(content, six.text_type):
-            content = content.encode()
+            content = content.encode("utf-8")
 
         try:
             oscrypto.asymmetric.rsa_pkcs1v15_verify(