diff --git a/src/PortAudio.jl b/src/PortAudio.jl
index dbd7958..50328ff 100644
--- a/src/PortAudio.jl
+++ b/src/PortAudio.jl
@@ -44,18 +44,20 @@ type PortAudioSink{T, U} <: SampleSink
     bufsize::Int
     buffer::Array{T, 2}
     transbuf::Array{T, 2}
+    waiters::Vector{Condition}
+    busy::Bool
 
     function PortAudioSink(eltype, rate, channels, bufsize)
         stream = Pa_OpenDefaultStream(0, channels, type_to_fmt[eltype], float(rate), bufsize)
-        writers = Condition[]
         buffer = Array(eltype, bufsize, channels)
         # as of portaudio 19.20140130 (which is the HomeBrew version as of 20160319)
         # noninterleaved data is not supported for the read/write interface on OSX
         transbuf = Array(eltype, channels, bufsize)
+        waiters = Condition[]
 
         Pa_StartStream(stream)
 
-        this = new(stream, channels, rate, bufsize, buffer, transbuf)
+        this = new(stream, channels, rate, bufsize, buffer, transbuf, waiters, false)
         finalizer(this, close)
 
         this
@@ -81,8 +83,17 @@ Base.eltype{T, U}(sink::PortAudioSink{T, U}) = T
 # end
 
 function SampleTypes.unsafe_write(sink::PortAudioSink, buf::SampleBuf)
+    if sink.busy
+        c = Condition()
+        push!(sink.waiters, c)
+        wait(c)
+        shift!(sink.waiters)
+    end
+
+    sink.busy = true
     total = nframes(buf)
     written = 0
+
     while written < total
         n = min(size(sink.transbuf, 2), total-written, Pa_GetStreamWriteAvailable(sink.stream))
         bufstart = 1+written
@@ -93,6 +104,11 @@ function SampleTypes.unsafe_write(sink::PortAudioSink, buf::SampleBuf)
         written += n
         sleep(0.005)
     end
+    sink.busy = false
+    if length(sink.waiters) > 0
+        # let the next task in line go
+        notify(sink.waiters[1])
+    end
 
     written
 end