diff --git a/src/FindFirstFunctions.jl b/src/FindFirstFunctions.jl
index 6322da8..c324303 100644
--- a/src/FindFirstFunctions.jl
+++ b/src/FindFirstFunctions.jl
@@ -233,7 +233,9 @@ end
 function (g::Guesser)(x)
     (; v, idx_prev, linear_lookup) = g
     if linear_lookup
-        f = (x - first(v)) / (last(v) - first(v))
+        δx = x - first(v)
+        iszero(δx) && return firstindex(v)
+        f = δx / (last(v) - first(v))
         if isinf(f)
             f > 0 ? lastindex(v) : firstindex(v)
         else
diff --git a/test/runtests.jl b/test/runtests.jl
index 1e49042..2d3a88b 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -39,5 +39,19 @@ using SafeTestsets, Test
         @test searchsortedfirstcorrelated(v, 4.0, guesser_linear) == 3
         @test searchsortedlastcorrelated(v, 4.0, guesser_prev) == 2
         @test guesser_prev.idx_prev[] == 2
+
+        # Edge case 
+        v1 = [42.0]
+        guesser = Guesser(v1)
+        @test guesser_linear.linear_lookup
+        @test guesser(100) == 1
+        @test guesser(42.0) == 1
+        @test guesser(0) == 1
+        @test searchsortedfirstcorrelated(v1, 0, guesser) == 1
+        @test searchsortedfirstcorrelated(v1, 100, guesser) == 1 + 1  # see searchsortedfirst
+        @test searchsortedfirstcorrelated(v1, 42.0, guesser) == 1
+        @test searchsortedlastcorrelated(v1, 0, guesser) == 1 - 1 # see searchsortedlast
+        @test searchsortedlastcorrelated(v1, 100, guesser) == 1
+        @test searchsortedlastcorrelated(v1, 42.0, guesser) == 1
     end
 end