diff --git a/src/StdLib.jl b/src/StdLib.jl
index 5eb4199..451b3f5 100644
--- a/src/StdLib.jl
+++ b/src/StdLib.jl
@@ -112,9 +112,10 @@ Base.cmp(a::String, b::CppBasicString) = cmp(a,String(b))
 
 # Make sure functions taking a C++ string as argument can also take a Julia string
 CxxWrapCore.map_julia_arg_type(x::Type{<:StdString}) = AbstractString
-StdLib.StdStringAllocated(x::String) = StdString(x,length(x))
-Base.cconvert(::Type{CxxWrapCore.ConstCxxRef{StdString}}, x::String) = StdString(x,length(x))
-Base.cconvert(::Type{StdLib.StdStringDereferenced}, x::String) = StdString(x,length(x))
+StdString(x::String) = StdString(x,ncodeunits(x))
+StdLib.StdStringAllocated(x::String) = StdString(x,ncodeunits(x))
+Base.cconvert(::Type{CxxWrapCore.ConstCxxRef{StdString}}, x::String) = StdString(x,ncodeunits(x))
+Base.cconvert(::Type{StdLib.StdStringDereferenced}, x::String) = StdString(x,ncodeunits(x))
 Base.unsafe_convert(::Type{CxxWrapCore.ConstCxxRef{StdString}}, x::StdString) = ConstCxxRef(x)
 
 function StdValArray(v::Vector{T}) where {T}
diff --git a/test/stdlib.jl b/test/stdlib.jl
index 90876aa..c1a465b 100644
--- a/test/stdlib.jl
+++ b/test/stdlib.jl
@@ -39,10 +39,10 @@ let s = StdString("foo")
 end
 
 let s = "\x01\x00\x02"
-    @test length(StdString(s)) == 1
+    @test length(StdString(s)) == 3
     @test length(StdString(s, length(s))) == 3
 
-    @test String(StdString(s)) != s
+    @test String(StdString(s)) == s
     @test String(StdString(s, length(s))) == s
 end