diff --git a/lib/ordered_set.h b/lib/ordered_set.h
index 1adfb8c5986..19747d20dd8 100644
--- a/lib/ordered_set.h
+++ b/lib/ordered_set.h
@@ -99,7 +99,7 @@ class ordered_set {
         // have a set of ordered_sets (or use ordered_set as a map key).
         auto it = a.data_map.begin();
         for (auto &el : data_map) {
-            if (it == a.data_map.end()) return true;
+            if (it == a.data_map.end()) return false;
             if (mapcmp()(el.first, it->first)) return true;
             if (mapcmp()(it->first, el.first)) return false;
             ++it; }
diff --git a/test/gtest/ordered_set.cpp b/test/gtest/ordered_set.cpp
index d844f919028..d921412acf3 100644
--- a/test/gtest/ordered_set.cpp
+++ b/test/gtest/ordered_set.cpp
@@ -93,4 +93,15 @@ TEST(ordered_set, set_intersect) {
     EXPECT_EQ(res, expect);
 }
 
+TEST(ordered_set, x_is_strict_prefix_of_y) {
+    ordered_set<unsigned> x;
+    x.insert(1);
+
+    ordered_set<unsigned> y;
+    y.insert(1);
+    y.insert(2);
+
+    EXPECT_LT(x, y);
+}
+
 }  // namespace Test