diff --git a/CHANGES/4127.doc.rst b/CHANGES/4127.doc.rst
new file mode 100644
index 00000000000..5ec427457f4
--- /dev/null
+++ b/CHANGES/4127.doc.rst
@@ -0,0 +1,3 @@
+Stopped ``Parameters:``, ``Returns:`` and other field-list labels in the
+rendered documentation from collapsing into a one-character-wide column by
+giving ``dl.field-list>dt`` a small ``min-width`` in the custom stylesheet.
diff --git a/docs/_static/css/logo-adjustments.css b/docs/_static/css/logo-adjustments.css
index b93746f65fb..d2419e35153 100644
--- a/docs/_static/css/logo-adjustments.css
+++ b/docs/_static/css/logo-adjustments.css
@@ -5,3 +5,13 @@
 .sphinxsidebarwrapper>p.logo>a>img.logo {
   width: 65%;
 }
+
+/*
+ * Prevent the "Parameters:", "Returns:", "Raises:" (and other field-list
+ * labels generated by Sphinx for ``:param:`` / ``:return:`` / ``:raise:``)
+ * from being squeezed into a one-character-wide column when the field
+ * body is long.  See aio-libs/aiohttp#4127.
+ */
+dl.field-list>dt {
+  min-width: 6em;
+}