diff --git a/src/include/interval-map/interval-map.hh b/src/include/interval-map/interval-map.hh
index ab3fb44..b518f24 100644
--- a/src/include/interval-map/interval-map.hh
+++ b/src/include/interval-map/interval-map.hh
@@ -35,7 +35,7 @@ public:
         if (insert_begin)
             it = underlying_.insert(it, {begin, val});
         // Get the proper upper-bound for `end`
-        it = (it == underlying_.end()) ? it : std::next(it);
+        it = (it == underlying_.end() || end < it->first) ? it : std::next(it);
         if (!(at_upper_bound(it) == end_val))
             underlying_.insert(it, {end, end_val});
     }
diff --git a/tests/unit/unit_test.cc b/tests/unit/unit_test.cc
index c429d29..53675c3 100644
--- a/tests/unit/unit_test.cc
+++ b/tests/unit/unit_test.cc
@@ -242,6 +242,12 @@ TEST_F(IntervalMapTest, fuzzing_003) {
     assign(-110, -10, 4);
 }
 
+TEST_F(IntervalMapTest, fuzzing_004) {
+    assign(-20, 120, 1);
+    assign(50, 110, 0);
+    assign(-120, 100, 0);
+}
+
 TEST_F(IntervalMapTest, randomized_test) {
     auto const seed = []() {
         std::random_device r;