diff --git a/roaring/roaring.go b/roaring/roaring.go
index 2de26d812..3d666056d 100644
--- a/roaring/roaring.go
+++ b/roaring/roaring.go
@@ -1340,9 +1340,9 @@ func (c *container) bitmapContains(v uint32) bool {
 	return (c.bitmap[v/64] & (1 << uint64(v%64))) != 0
 }
 
-//runBinSearch uses a binary search of the runs and returns the index of nearest
-//run.
-func binSearchRuns(v uint32, a []interval32) (int, bool) {
+// runBinSearch returns the index of the run containing v, and true, when v is contained;
+// or the index of the next run starting after v, and false, when v is not contained.
+func runBinSearch(v uint32, a []interval32) (int, bool) {
 	i := sort.Search(len(a),
 		func(i int) bool { return a[i].last >= v })
 	if i < len(a) {
diff --git a/roaring/roaring_internal_test.go b/roaring/roaring_internal_test.go
index 400f99b66..0c4bf8e0d 100644
--- a/roaring/roaring_internal_test.go
+++ b/roaring/roaring_internal_test.go
@@ -1692,3 +1692,67 @@ func TestRunBinSearchContains(t *testing.T) {
 		}
 	}
 }
+
+func TestRunBinSearch(t *testing.T) {
+	tests := []struct {
+		runs   []interval32
+		search uint32
+		exp    bool
+		expi   int
+	}{
+		{
+			runs:   []interval32{{2, 10}, {50, 60}, {80, 90}},
+			search: 1,
+			exp:    false,
+			expi:   0,
+		},
+		{
+			runs:   []interval32{{2, 10}, {50, 60}, {80, 90}},
+			search: 2,
+			exp:    true,
+			expi:   0,
+		},
+		{
+			runs:   []interval32{{2, 10}, {50, 60}, {80, 90}},
+			search: 5,
+			exp:    true,
+			expi:   0,
+		},
+		{
+			runs:   []interval32{{2, 10}, {50, 60}, {80, 90}},
+			search: 10,
+			exp:    true,
+			expi:   0,
+		},
+		{
+			runs:   []interval32{{2, 10}, {50, 60}, {80, 90}},
+			search: 20,
+			exp:    false,
+			expi:   1,
+		},
+		{
+			runs:   []interval32{{2, 10}, {50, 60}, {80, 90}},
+			search: 55,
+			exp:    true,
+			expi:   1,
+		},
+		{
+			runs:   []interval32{{2, 10}, {50, 60}, {80, 90}},
+			search: 70,
+			exp:    false,
+			expi:   2,
+		},
+		{
+			runs:   []interval32{{2, 10}, {50, 60}, {80, 90}},
+			search: 100,
+			exp:    false,
+			expi:   3,
+		},
+	}
+	for i, test := range tests {
+		idx, contains := runBinSearch(test.search, test.runs)
+		if !(test.exp == contains && test.expi == idx) {
+			t.Fatalf("test #%v expected (%v, %v) but got (%v, %v)", i, test.exp, test.expi, contains, idx)
+		}
+	}
+}