diff --git a/.travis.yml b/.travis.yml
index c5809d07..65dea99f 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -135,7 +135,7 @@ script:
     - env LLVM_PROFILE_FILE="$PWD/unittest.profraw" make VERBOSE=1 unittest
     - sudo make install
       # TODO: use DEVEL_COVER_OPTIONS for https://metacpan.org/pod/Devel::Cover
-    - env LLVM_PROFILE_FILE="$PWD/inttest.profraw" ZNC_MODPERL_COVERAGE_OPTS="-db,$PWD/cover_db" make VERBOSE=1 inttest
+    - env LLVM_PROFILE_FILE="$PWD/inttest.profraw" ZNC_MODPERL_COVERAGE_OPTS="-db,$PWD/cover_db" PYTHONWARNINGS=error make VERBOSE=1 inttest
     - /usr/local/bin/znc --version
 after_success:
     - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then ~/perl5/bin/cover --no-gcov --report=clover; fi
diff --git a/modules/modpython.cpp b/modules/modpython.cpp
index dfe53b5b..7bc76fc5 100644
--- a/modules/modpython.cpp
+++ b/modules/modpython.cpp
@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+#define PY_SSIZE_T_CLEAN
 #include <Python.h>
 
 #include <znc/Chan.h>
@@ -455,7 +456,7 @@ CBSOCK(ConnectionRefused);
 void CPySocket::ReadData(const char* data, size_t len) {
     PyObject* pyRes =
         PyObject_CallMethod(m_pyObj, const_cast<char*>("OnReadData"),
-                            const_cast<char*>("y#"), data, (int)len);
+                            const_cast<char*>("y#"), data, (Py_ssize_t)len);
     CHECKCLEARSOCK("OnReadData");
 }