diff --git a/src/core/lib/iomgr/ev_epoll_linux.c b/src/core/lib/iomgr/ev_epoll_linux.c
index 8381f4a63a47b28f89fcab91ea6e33f369c88a01..db51ec49392a8b91a8f464f438a9c3c274e9c401 100644
--- a/src/core/lib/iomgr/ev_epoll_linux.c
+++ b/src/core/lib/iomgr/ev_epoll_linux.c
@@ -1711,6 +1711,12 @@ retry:
             "pollset_add_fd: Raced creating new polling island. pi_new: %p "
             "(fd: %d, pollset: %p)",
             (void *)pi_new, fd->fd, (void *)pollset);
+
+        /* No need to lock 'pi_new' here since this is a new polling island and
+         * no one has a reference to it yet */
+        polling_island_remove_all_fds_locked(pi_new, true, &error);
+
+        /* Ref and unref so that the polling island gets deleted during unref */
         PI_ADD_REF(pi_new, "dance_of_destruction");
         PI_UNREF(exec_ctx, pi_new, "dance_of_destruction");
         goto retry;
diff --git a/tools/run_tests/build_python.sh b/tools/run_tests/build_python.sh
index b786c479f3660fea4597b3254ae5446c6601b996..54e2fe534789c9cce9168ecab585d243e11322f1 100755
--- a/tools/run_tests/build_python.sh
+++ b/tools/run_tests/build_python.sh
@@ -39,6 +39,14 @@ cd $(dirname $0)/../..
 
 PLATFORM=`uname -s`
 
+function is_msys() {
+  if [ "${PLATFORM/MSYS}" != "$PLATFORM" ]; then
+    echo true
+  else
+    exit 1
+  fi
+}
+
 function is_mingw() {
   if [ "${PLATFORM/MINGW}" != "$PLATFORM" ]; then
     echo true
@@ -108,6 +116,12 @@ VENV=${2:-$(venv $PYTHON)}
 VENV_RELATIVE_PYTHON=${3:-$(venv_relative_python)}
 TOOLCHAIN=${4:-$(toolchain)}
 
+if [ $(is_msys) ]; then
+  echo "MSYS doesn't directly provide the right compiler(s);"
+  echo "switch to a MinGW shell."
+  exit 1
+fi
+
 ROOT=`pwd`
 export CFLAGS="-I$ROOT/include -std=gnu99 -fno-wrapv $CFLAGS"
 export GRPC_PYTHON_BUILD_WITH_CYTHON=1