diff --git a/src/strings.jl b/src/strings.jl
index eea55a64..04fc176a 100644
--- a/src/strings.jl
+++ b/src/strings.jl
@@ -80,6 +80,7 @@ end
 
 @doc raw"""
     sub(i::T) where T<:Real
+    sub(str::String)
 
 Subscript notation for integers, rational numbers and a *subset* of lowercase characters ('a','e','h','k','l','m','n','o','p','r','s','t','x')
 #### Examples:
diff --git a/test/runtests.jl b/test/runtests.jl
index 3c58fc4a..056934e1 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -52,6 +52,7 @@ using Test
     @test grid_integration(real(ZH1s_generic) .^ 2, 1, grid.N, grid) ≈ 1.0
     @test sup(-5 // 2) == "⁻⁵ᐟ²"
     @test sub(-5 // 2) == "₋₅⸝₂"
+    @test sub("e") == "ₑ"
     @test frac(-5 // 2) == "-⁵/₂"
     @test strRational(-5) == "-5"
     @test strRational(-5 // 2) == "-5/2"