diff --git a/base/io.jl b/base/io.jl
index 45faa621f8fa6..dc588a8efd0e9 100644
--- a/base/io.jl
+++ b/base/io.jl
@@ -1178,8 +1178,13 @@ julia> io = IOBuffer("JuliaLang is a GitHub organization.");
 julia> countlines(io)
 1
 
+julia> eof(io) # counting lines moves the file pointer
+true
+
+julia> io = IOBuffer("JuliaLang is a GitHub organization.");
+
 julia> countlines(io, eol = '.')
-0
+1
 ```
 """
 function countlines(io::IO; eol::AbstractChar='\n')