diff --git a/testinfra/backend/base.py b/testinfra/backend/base.py
index a1a3be2b..1d7a84cc 100644
--- a/testinfra/backend/base.py
+++ b/testinfra/backend/base.py
@@ -17,6 +17,7 @@
 import shlex
 import subprocess
 import urllib.parse
+from typing import Any, Optional
 
 logger = logging.getLogger("testinfra")
 
@@ -26,13 +27,13 @@
 class CommandResult:
     def __init__(
         self,
-        backend,
-        exit_status,
-        command,
-        stdout_bytes,
-        stderr_bytes,
-        stdout=None,
-        stderr=None,
+        backend: "BaseBackend",
+        exit_status: int,
+        command: bytes,
+        stdout_bytes: bytes,
+        stderr_bytes: bytes,
+        stdout: Optional[str] = None,
+        stderr: Optional[str] = None,
     ):
         self.exit_status = exit_status
         self._stdout_bytes = stdout_bytes
@@ -44,7 +45,7 @@ def __init__(
         super().__init__()
 
     @property
-    def succeeded(self):
+    def succeeded(self) -> bool:
         """Returns whether the command was successful
 
         >>> host.run("true").succeeded
@@ -53,7 +54,7 @@ def succeeded(self):
         return self.exit_status == 0
 
     @property
-    def failed(self):
+    def failed(self) -> bool:
         """Returns whether the command failed
 
         >>> host.run("false").failed
@@ -62,7 +63,7 @@ def failed(self):
         return self.exit_status != 0
 
     @property
-    def rc(self):
+    def rc(self) -> int:
         """Gets the returncode of a command
 
         >>> host.run("true").rc
@@ -71,30 +72,30 @@ def rc(self):
         return self.exit_status
 
     @property
-    def stdout(self):
+    def stdout(self) -> str:
         if self._stdout is None:
             self._stdout = self._backend.decode(self._stdout_bytes)
         return self._stdout
 
     @property
-    def stderr(self):
+    def stderr(self) -> str:
         if self._stderr is None:
             self._stderr = self._backend.decode(self._stderr_bytes)
         return self._stderr
 
     @property
-    def stdout_bytes(self):
+    def stdout_bytes(self) -> bytes:
         if self._stdout_bytes is None:
             self._stdout_bytes = self._backend.encode(self._stdout)
         return self._stdout_bytes
 
     @property
-    def stderr_bytes(self):
+    def stderr_bytes(self) -> bytes:
         if self._stderr_bytes is None:
             self._stderr_bytes = self._backend.encode(self._stderr)
         return self._stderr_bytes
 
-    def __repr__(self):
+    def __repr__(self) -> str:
         return (
             "CommandResult(command={!r}, exit_status={}, stdout={!r}, " "stderr={!r})"
         ).format(
@@ -112,7 +113,14 @@ class BaseBackend(metaclass=abc.ABCMeta):
     HAS_RUN_ANSIBLE = False
     NAME: str
 
-    def __init__(self, hostname, sudo=False, sudo_user=None, *args, **kwargs):
+    def __init__(
+        self,
+        hostname: str,
+        sudo: bool = False,
+        sudo_user: Optional[bool] = None,
+        *args: Any,
+        **kwargs: Any,
+    ):
         self._encoding = None
         self._host = None
         self.hostname = hostname
@@ -245,7 +253,7 @@ def parse_containerspec(containerspec):
             user, name = name.split("@", 1)
         return name, user
 
-    def get_encoding(self) -> str:
+    def get_encoding(self):
         encoding = None
         for python in ("python3", "python"):
             cmd = self.run(
@@ -271,19 +279,19 @@ def encoding(self):
             self._encoding = self.get_encoding()
         return self._encoding
 
-    def decode(self, data):
+    def decode(self, data: bytes) -> str:
         try:
             return data.decode("ascii")
         except UnicodeDecodeError:
             return data.decode(self.encoding)
 
-    def encode(self, data):
+    def encode(self, data: str) -> bytes:
         try:
             return data.encode("ascii")
         except UnicodeEncodeError:
             return data.encode(self.encoding)
 
-    def result(self, *args, **kwargs):
+    def result(self, *args: Any, **kwargs: Any) -> CommandResult:
         result = CommandResult(self, *args, **kwargs)
         logger.debug("RUN %s", result)
         return result