diff --git a/.github/workflows/lint.yml b/.github/workflows/lint.yml
index 31f7efa..fea7e62 100644
--- a/.github/workflows/lint.yml
+++ b/.github/workflows/lint.yml
@@ -48,9 +48,8 @@ jobs:
           cache-dependency-path: |
             setup.py
 
-      # all extras are installed to test
       - name: Install dependencies
-        run: python -m pip install -e ".[dev]" -e ".[docs]"
+        run: python -m pip install -r requirements.txt -e ".[dev]" -e ".[docs]"
 
       - name: Set up pyright
         run: echo "PYRIGHT_VERSION=$(python -c 'import pyright; print(pyright.__pyright_version__)')" >> $GITHUB_ENV
@@ -77,6 +76,29 @@ jobs:
           no-comments: true
           warnings: true
 
+  mypy:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ["3.10"]
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v3
+
+      - name: Set up python ${{ matrix.python-version }}
+        uses: actions/setup-python@v4
+        with:
+          python-version: ${{ matrix.python-version }}
+          cache: pip
+          cache-dependency-path: |
+            setup.py
+
+      - name: Install dependencies
+        run: python -m pip install -r requirements.txt -e ".[dev]" -e ".[docs]"
+
+      - name: Run mypy
+        run: mypy .
+
   slotscheck:
     runs-on: ubuntu-latest
 
diff --git a/pyproject.toml b/pyproject.toml
index e7e32d6..8d7680c 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -67,3 +67,15 @@ reportUnsupportedDunderAll = true
 reportUnusedVariable = true
 reportUnnecessaryComparison = true
 reportUnnecessaryTypeIgnoreComment = true
+
+
+[tool.mypy]
+python_version = "3.10"
+namespace_packages = true
+
+
+[[tool.mypy.overrides]]
+module = [
+    "setuptools.*",
+]
+ignore_missing_imports = true
diff --git a/setup.py b/setup.py
index c4f622c..6cf7af7 100644
--- a/setup.py
+++ b/setup.py
@@ -48,6 +48,7 @@ def requirements():
         "pyright==1.1.244",
         "tox==3.24.5",
         "pytest==7.1.2",
+        "mypy==0.982",
     ],
 }
 
diff --git a/table2ascii/annotations.py b/table2ascii/annotations.py
index cb78bdd..241e787 100644
--- a/table2ascii/annotations.py
+++ b/table2ascii/annotations.py
@@ -1,11 +1,10 @@
+import sys
 from abc import abstractmethod
 from typing import TYPE_CHECKING
 
-try:
-    # Python 3.8+
+if sys.version_info >= (3, 8):
     from typing import Protocol, runtime_checkable
-except ImportError:
-    # Python 3.7
+else:
     from typing_extensions import Protocol, runtime_checkable
 
 if TYPE_CHECKING:
@@ -16,8 +15,6 @@
 class SupportsStr(Protocol):
     """An ABC with one abstract method __str__."""
 
-    __slots__ = ()
-
     @abstractmethod
     def __str__(self) -> str:
         pass
diff --git a/table2ascii/preset_style.py b/table2ascii/preset_style.py
index 460d7b2..5732219 100644
--- a/table2ascii/preset_style.py
+++ b/table2ascii/preset_style.py
@@ -43,7 +43,7 @@ class PresetStyle:
     ascii_minimalist = TableStyle.from_string(" ---  |  ===  ---  -- ")
     ascii_borderless = TableStyle.from_string("      |  -            ")
     ascii_simple = TableStyle.from_string(" =    |  =            ")
-    ascii_rounded = TableStyle.from_string("/===\|| |=|=||-|-|\|=/")
-    ascii_rounded_box = TableStyle.from_string("/===\||||=||||-|||\||/")
+    ascii_rounded = TableStyle.from_string(r"/===\|| |=|=||-|-|\|=/")
+    ascii_rounded_box = TableStyle.from_string(r"/===\||||=||||-|||\||/")
     markdown = TableStyle.from_string("     ||||-|||         ")
     plain = TableStyle.from_string("                      ")
diff --git a/table2ascii/py.typed b/table2ascii/py.typed
new file mode 100644
index 0000000..356bf16
--- /dev/null
+++ b/table2ascii/py.typed
@@ -0,0 +1 @@
+# Marker file for PEP 561. The table2ascii package uses inline types.
\ No newline at end of file
diff --git a/table2ascii/table_to_ascii.py b/table2ascii/table_to_ascii.py
index 7b8ab81..8a00449 100644
--- a/table2ascii/table_to_ascii.py
+++ b/table2ascii/table_to_ascii.py
@@ -96,23 +96,20 @@ def __auto_column_widths(self) -> List[int]:
             The minimum number of characters needed for each column
         """
 
-        def widest_line(text: str) -> int:
+        def widest_line(value: SupportsStr) -> int:
             """Returns the width of the longest line in a multi-line string"""
+            text = str(value)
             return max(len(line) for line in text.splitlines()) if len(text) else 0
 
         column_widths = []
         # get the width necessary for each column
         for i in range(self.__columns):
-            # col_widest returns the width of the widest line in the ith cell of a given list
-            col_widest: Callable[[List[SupportsStr], int], int] = lambda row, i=i: widest_line(
-                str(row[i])
-            )
             # number of characters in column of i of header, each body row, and footer
-            header_size = col_widest(self.__header) if self.__header else 0
-            body_size = map(col_widest, self.__body) if self.__body else [0]
-            footer_size = col_widest(self.__footer) if self.__footer else 0
+            header_size = widest_line(self.__header[i]) if self.__header else 0
+            body_size = max(widest_line(row[i]) for row in self.__body) if self.__body else 0
+            footer_size = widest_line(self.__footer[i]) if self.__footer else 0
             # get the max and add 2 for padding each side with a space
-            column_widths.append(max(header_size, *body_size, footer_size) + 2)
+            column_widths.append(max(header_size, body_size, footer_size) + 2)
         return column_widths
 
     def __pad(self, cell_value: SupportsStr, width: int, alignment: Alignment) -> str: