2 files changed, 14 insertions, 1 deletions
diff --git a/absl/algorithm/container.h b/absl/algorithm/container.h
index 3c4fd733..bb3d1c7c 100644
--- a/absl/algorithm/container.h
+++ b/absl/algorithm/container.h
@@ -351,7 +351,9 @@ c_mismatch(C1& c1, C2& c2) {
   auto last2 = container_algorithm_internal::c_end(c2);
 
   for (; first1 != last1 && first2 != last2; ++first1, (void)++first2) {
-    if (*first1 != *first2) {
+    // Negates equality because Cpp17EqualityComparable doesn't require clients
+    // to overload both `operator==` and `operator!=`.
+    if (!(*first1 == *first2)) {
       break;
     }
   }
diff --git a/absl/algorithm/container_test.cc b/absl/algorithm/container_test.cc
index fb940560..605afc80 100644
--- a/absl/algorithm/container_test.cc
+++ b/absl/algorithm/container_test.cc
@@ -183,6 +183,17 @@ TEST_F(NonMutatingTest, Mismatch) {
     EXPECT_EQ(result.first, sequence_.end());
     EXPECT_EQ(result.second, std::prev(vector_.end()));
   }
+  {
+    struct NoNotEquals {
+      constexpr bool operator==(NoNotEquals) const { return true; }
+      constexpr bool operator!=(NoNotEquals) const = delete;
+    };
+    std::vector<NoNotEquals> first;
+    std::list<NoNotEquals> second;
+
+    // Check this still compiles.
+    absl::c_mismatch(first, second);
+  }
 }
 
 TEST_F(NonMutatingTest, MismatchWithPredicate) {