diff --git a/base/io.jl b/base/io.jl
index 39479084f28c3..12480a9dd1848 100644
--- a/base/io.jl
+++ b/base/io.jl
@@ -154,8 +154,6 @@ unsafe_read(io::AbstractPipe, p::Ptr{UInt8}, nb::UInt) = unsafe_read(pipe_reader
 read(io::AbstractPipe) = read(pipe_reader(io))
 readuntil(io::AbstractPipe, arg::UInt8)          = readuntil(pipe_reader(io), arg)
 readuntil(io::AbstractPipe, arg::Char)           = readuntil(pipe_reader(io), arg)
-readuntil(io::AbstractPipe, arg::AbstractString) = readuntil(pipe_reader(io), arg)
-readuntil(io::AbstractPipe, arg)                 = readuntil(pipe_reader(io), arg)
 readavailable(io::AbstractPipe) = readavailable(pipe_reader(io))
 
 isreadable(io::AbstractPipe) = isreadable(pipe_reader(io))
@@ -499,7 +497,7 @@ function readuntil(s::IO, delim::Char)
 end
 
 function readuntil(s::IO, delim::T) where T
-    out = T[]
+    out = (T === UInt8 ? StringVector(0) : Vector{T}())
     while !eof(s)
         c = read(s, T)
         push!(out, c)
@@ -510,41 +508,80 @@ function readuntil(s::IO, delim::T) where T
     return out
 end
 
+function _rfind_sub_c(target, endc, endstate)
+    # find the largest i (< endstate) such that "target[(end - i + 1):(end - 1)] * c" == "target[1:i]"
+    # (equivalently, find the smallest tii' such that "target[tii':(end - 1)] * c" == "target[1:(end - tii' + 1)]")
+    # this assumes that the `target` iterator is pure and supports equality comparison for its state
+    # and that endstate is a valid state for target
+    tii = start(target)
+    i = start(target)
+    ti = tii
+    while tii != endstate
+        c, i = next(target, i)
+        tc, ti = next(target, ti)
+        if ti == endstate
+            if c == endc
+                return i
+            end
+        else
+            if tc == c
+                continue
+            end
+        end
+        tii = next(target, tii)[2]
+        i = start(target)
+        ti = tii
+    end
+    return start(target)
+end
+
 function readuntil(s::IO, target::AbstractString)
-    l = length(target)
-    if l == 0
+    ti = start(target)
+    if done(target, ti)
         return ""
     end
-    t = collect(target)
-    backtrack = zeros(Int, l)
-    for i = 2:l
-        b = backtrack[i - 1] + 1
-        if t[i] == t[b]
-            backtrack[i] = b
-        end
+    c1, tc1 = next(target, ti)
+    if done(target, tc1) && c1 < Char(0x80)
+        return readuntil_string(s, c1 % UInt8)
     end
     out = IOBuffer()
-    i = 0
     while !eof(s)
         c = read(s, Char)
         write(out, c)
-        while i != 0 && c != t[i + 1]
-            if i > 0
-                i = backtrack[i]
-            else
-                i = 0
-            end
-        end
-        if c == t[i + 1]
-            i += 1
-        end
-        if i == l
-            break
+        tc, ti = next(target, ti)
+        if c == tc
+            done(target, ti) && break
+        else
+            ti = _rfind_sub_c(target, c, ti)
         end
     end
     return String(take!(out))
 end
 
+function readuntil(s::IO, target::String)
+    ti = start(target)
+    if done(target, ti)
+        return ""
+    end
+    c1, tc1 = next(target, ti)
+    if done(target, tc1) && c1 < Char(0x80)
+        return readuntil_string(s, c1 % UInt8)
+    end
+    targetb = Vector{UInt8}(target) # convert String to a utf8-byte-iterator
+    out = StringVector(0)
+    while !eof(s)
+        c = read(s, UInt8)
+        push!(out, c)
+        tc, ti = next(targetb, ti)
+        if c == tc
+            done(targetb, ti) && break
+        else
+            ti = _rfind_sub_c(targetb, c, ti)
+        end
+    end
+    return String(out)
+end
+
 """
     readchomp(x)
 
@@ -594,6 +631,7 @@ function read(s::IO, nb::Integer = typemax(Int))
 end
 
 read(s::IO, ::Type{String}) = String(read(s))
+read(s::IO, T::Type) = error("The IO stream does not support reading objects of type $T.")
 
 ## high-level iterator interfaces ##
 
diff --git a/test/read.jl b/test/read.jl
index 155c187e2c0b1..07bce1054968b 100644
--- a/test/read.jl
+++ b/test/read.jl
@@ -94,12 +94,6 @@ s = io(text)
 close(s)
 push!(l, ("PipeEndpoint", io))
 
-
-# readuntil
-@test readuntil(IOBuffer("aaabc"), "aab") == "aaab"
-@test readuntil(IOBuffer("assassassinass"), "assassin") == "assassassin"
-
-
 #FIXME See https://github.com/JuliaLang/julia/issues/14747
 #      Reading from open(::Command) seems to deadlock on Linux/Travis
 #=
@@ -141,10 +135,24 @@ end
 
 verbose = false
 
-
 for (name, f) in l
     local f
-    io = ()->(s=f(text); push!(open_streams, s); s)
+    local function io(text=text)
+        local s = f(text)
+        push!(open_streams, s)
+        return s
+    end
+
+    verbose && println("$name readuntil...")
+    for (t, s, m) in [
+            ("aaabc", "aab", "aaab"),
+            ("assassassinass", "assassin", "assassassin")]
+        local t, s, m
+        @test readuntil(io(t), s) == m
+
+        s = SubString(s, start(s), endof(s))
+        @test readuntil(io(t), s) == m
+    end
 
     write(filename, text)