diff --git a/changelog.d/1390.misc.rst b/changelog.d/1390.misc.rst
new file mode 100644
index 0000000000..5e4fb11488
--- /dev/null
+++ b/changelog.d/1390.misc.rst
@@ -0,0 +1 @@
+Validation of Description field now is more lenient, emitting a warning and mangling the value to be valid (replacing newlines with spaces).
diff --git a/setuptools/dist.py b/setuptools/dist.py
index 2d0aac333d..172d66b1f4 100644
--- a/setuptools/dist.py
+++ b/setuptools/dist.py
@@ -121,7 +121,9 @@ def _read_list(name):
 def single_line(val):
     # quick and dirty validation for description pypa/setuptools#1390
     if '\n' in val:
-        raise ValueError("newlines not allowed")
+        # TODO after 2021-07-31: Replace with `raise ValueError("newlines not allowed")`
+        warnings.UserWarning("newlines not allowed and will break in the future")
+        val = val.replace('\n', ' ')
     return val