diff --git a/base/sort.jl b/base/sort.jl
index 8a3d2e2871cfe..e69ed8cfa61a0 100644
--- a/base/sort.jl
+++ b/base/sort.jl
@@ -519,7 +519,7 @@ function sort!(v::AbstractVector, lo::Integer, hi::Integer, ::InsertionSortAlg,
         x = v[i]
         while j > lo
             y = v[j-1]
-            if !lt(o, x, y)
+            if !(lt(o, x, y)::Bool)
                 break
             end
             v[j] = y