diff --git a/src/os.cpp b/src/os.cpp
index f0134d3..7eee36e 100644
--- a/src/os.cpp
+++ b/src/os.cpp
@@ -185,13 +185,12 @@ static void *run_pthread(void *userdata) {
     return NULL;
 }
 static void emit_rtprio_warning(void) {
-    static bool seen = false;
-    if (seen)
-        return;
-    seen = true;
-    fprintf(stderr, "warning: unable to set high priority thread: Operation not permitted\n");
-    fprintf(stderr, "See https://github.com/andrewrk/genesis/wiki/"
-            "warning:-unable-to-set-high-priority-thread:-Operation-not-permitted\n");
+    static atomic_flag seen = ATOMIC_FLAG_INIT;
+    if (!seen.test_and_set()) {
+        fprintf(stderr, "warning: unable to set high priority thread: Operation not permitted\n");
+        fprintf(stderr, "See https://github.com/andrewrk/genesis/wiki/"
+                "warning:-unable-to-set-high-priority-thread:-Operation-not-permitted\n");
+    }
 }
 #endif
 
diff --git a/src/soundio.h b/src/soundio.h
index 11ecc6a..22e158b 100644
--- a/src/soundio.h
+++ b/src/soundio.h
@@ -509,11 +509,12 @@ int soundio_outstream_fill_with_silence(struct SoundIoOutStream *outstream);
 int soundio_outstream_free_count(struct SoundIoOutStream *outstream);
 
 // Call this function when you are ready to begin writing to the device buffer.
-// `outstream` - (in) The output stream you want to write to.
-// `areas` - (out) The memory addresses you can write data to.
-// `frame_count` - (in/out) Provide the number of frames you want to write.
-// returned will be the number of frames you actually can write. If this number
-// is greater than zero, you must call this function again.
+//  * `outstream` - (in) The output stream you want to write to.
+//  * `areas` - (out) The memory addresses you can write data to. It is OK to
+//     modify the pointers if that helps you iterate.
+//  * `frame_count` - (in/out) Provide the number of frames you want to write.
+//    Returned will be the number of frames you actually can write. If this
+//    number is greater than zero, you must call this function again.
 int soundio_outstream_begin_write(struct SoundIoOutStream *outstream,
         struct SoundIoChannelArea **areas, int *frame_count);