diff --git a/src/config/__init__.py b/src/config/__init__.py
index c493d61..f50d33b 100644
--- a/src/config/__init__.py
+++ b/src/config/__init__.py
@@ -26,7 +26,7 @@
 from ._version import __version__, __version_tuple__  # noqa: F401
 from .configuration import Configuration
 from .configuration_set import ConfigurationSet
-from .helpers import InterpolateEnumType, InterpolateType
+from .helpers import InterpolateEnumType, InterpolateType, parse_env_line
 
 
 def config(
@@ -586,9 +586,7 @@ def _reload(
                 data = data.read()
         data = cast(str, data)
         result: Dict[str, Any] = dict(
-            (y.strip() for y in x.split("=", 1))  # type: ignore
-            for x in data.splitlines()
-            if x
+            parse_env_line(x) for x in data.splitlines() if x and not x.startswith("#")
         )
 
         result = {
@@ -613,6 +611,8 @@ def config_from_dotenv(
 ) -> Configuration:
     """Create a [Configuration][config.configuration.Configuration] instance from a .env type file.
 
+    Lines starting with a # are ignored and treated as comments.
+
     Params:
         data: path to a .env type file or contents.
         read_from_file: whether to read from a file path or to interpret.
diff --git a/src/config/helpers.py b/src/config/helpers.py
index 54afcfa..2db70e7 100644
--- a/src/config/helpers.py
+++ b/src/config/helpers.py
@@ -212,3 +212,12 @@ def interpolate_object(
             return [interpolate_object(attr, x, d, method) for x in obj]
     else:
         return obj
+
+
+def parse_env_line(line: str) -> Tuple[str, str]:
+    """Split an env line into variable and value."""
+    try:
+        key, value = tuple(y.strip() for y in line.split("=", 1))
+    except ValueError:
+        raise ValueError("Invalid line %s" % line) from None
+    return key.strip(), value.strip()
diff --git a/tests/test_dotenv.py b/tests/test_dotenv.py
index b6e7c84..d492914 100644
--- a/tests/test_dotenv.py
+++ b/tests/test_dotenv.py
@@ -1,3 +1,4 @@
+import pytest
 from config import config_from_dotenv, config_from_dict
 import tempfile
 
@@ -17,6 +18,14 @@
 PREFIX__KEY4__C = 3
 """
 
+DOTENV_WITH_COMMENTS = """
+# key 1
+KEY1 = abc
+# key 2
+KEY2 = def
+# key 3
+KEY3 = 1.1
+"""
 
 DICT = {
     "key1": "abc",
@@ -83,3 +92,21 @@ def test_load_dotenv():  # type: ignore
     cfg = config_from_dotenv(DOTENV_WITH_PREFIXES, lowercase_keys=True, prefix="PREFIX")
     print(cfg.as_dict())
     assert cfg == config_from_dict(DICT_WITH_PREFIXES)
+
+
+def test_load_dotenv_comments():  # type: ignore
+    cfg = config_from_dotenv(DOTENV_WITH_COMMENTS, lowercase_keys=True)
+    assert cfg == config_from_dict(dict((k, str(v)) for k, v in DICT.items()))
+
+
+def test_load_dotenv_comments_invalid():  # type: ignore
+    invalid = """
+# key 1
+VALID=1
+## key2
+INVALID
+"""
+    with pytest.raises(ValueError) as err:
+        config_from_dotenv(invalid, lowercase_keys=True)
+    assert 'Invalid line INVALID' in str(err)
+
diff --git a/tests/test_issues.py b/tests/test_issues.py
index 4337991..3acd591 100644
--- a/tests/test_issues.py
+++ b/tests/test_issues.py
@@ -1,9 +1,11 @@
+import pytest
 from config import (
     Configuration,
     ConfigurationSet,
     EnvConfiguration,
     config,
     config_from_dict,
+    config_from_dotenv,
 )
 
 
@@ -78,3 +80,11 @@ def test_issue_79():  # type: ignore
     conf.update(data)
 
     assert conf["abc.def"] == "ghi"
+
+
+def test_issue_100():  # type: ignore
+    invalid = """# key 1\nVALID=1\n## key2\nINVALID\n"""
+    with pytest.raises(ValueError) as err:
+        config_from_dotenv(invalid, lowercase_keys=True)
+    assert 'Invalid line INVALID' in str(err)
+