diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 167cb88b59206796c04c96b41e55287ed9e3a5a4..d899c69940d977a07410ebb434d54671df4840a3 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,9 @@
+2020-05-23  Patrick Palka  <ppalka@redhat.com>
+
+	PR libstdc++/93978
+	* testsuite/std/ranges/adaptors/93978.cc: Add -Wall to
+	dg-additional-options.  Avoid unused-but-set-variable warning.
+
 2020-05-23  Jonathan Wakely  <jwakely@redhat.com>
 
 	PR libstdc++/95289
diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/93978.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/93978.cc
index a0152ec0532f17c6803c5709fbeb2407c83e20ab..82b82b0a5be962631211d9d7944943dc87113955 100644
--- a/libstdc++-v3/testsuite/std/ranges/adaptors/93978.cc
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/93978.cc
@@ -16,7 +16,7 @@
 // <http://www.gnu.org/licenses/>.
 
 // { dg-options "-std=gnu++2a" }
-// { dg-additional-options "-O" }
+// { dg-additional-options "-O -Wall" }
 // { dg-do compile { target c++2a } }
 
 #include <ranges>
@@ -25,11 +25,12 @@
 namespace ranges = std::ranges;
 namespace views = std::views;
 
-void
+auto
 test()
 {
   std::vector<std::string> x = {""};
   auto i = std::counted_iterator(x.begin(), 1);
   auto r = ranges::subrange{i, std::default_sentinel};
   auto v = r | views::join;
+  return v;
 }