diff --git a/include/portaudio.h b/include/portaudio.h
index 0c5b6a4..5d84731 100644
--- a/include/portaudio.h
+++ b/include/portaudio.h
@@ -849,7 +849,10 @@ typedef int PaStreamCallback(
  outputParameters must be NULL for input-only streams.
 
  @param sampleRate The desired sampleRate. For full-duplex streams it is the
- sample rate for both input and output
+ sample rate for both input and output. Note that the actual sampleRate
+ may differ very slightly from the desired rate because of hardware limitations.
+ The exact rate can be queried using Pa_GetStreamInfo(). If nothing close
+ to the desired sampleRate is available then the open will fail and return an error.
 
  @param framesPerBuffer The number of frames passed to the stream callback
  function, or the preferred block granularity for a blocking read/write stream.