diff --git a/dlls/wineoss.drv/mmdevdrv.c b/dlls/wineoss.drv/mmdevdrv.c
index 2ea3c80f3ca..a2f75d7a479 100644
--- a/dlls/wineoss.drv/mmdevdrv.c
+++ b/dlls/wineoss.drv/mmdevdrv.c
@@ -783,7 +783,7 @@ static HRESULT WINAPI AudioClient_GetBufferSize(IAudioClient3 *iface,
         UINT32 *frames)
 {
     ACImpl *This = impl_from_IAudioClient3(iface);
-    struct oss_stream *stream = This->stream;
+    struct get_buffer_size_params params;
 
     TRACE("(%p)->(%p)\n", This, frames);
 
@@ -793,15 +793,13 @@ static HRESULT WINAPI AudioClient_GetBufferSize(IAudioClient3 *iface,
     if(!This->stream)
         return AUDCLNT_E_NOT_INITIALIZED;
 
-    oss_lock(stream);
-
-    *frames = stream->bufsize_frames;
+    params.stream = This->stream;
+    params.size = frames;
 
+    OSS_CALL(get_buffer_size, &params);
     TRACE("buffer size: %u\n", *frames);
 
-    oss_unlock(stream);
-
-    return S_OK;
+    return params.result;
 }
 
 static HRESULT WINAPI AudioClient_GetStreamLatency(IAudioClient3 *iface,
diff --git a/dlls/wineoss.drv/oss.c b/dlls/wineoss.drv/oss.c
index 628d0c5818a..fdad419abfa 100644
--- a/dlls/wineoss.drv/oss.c
+++ b/dlls/wineoss.drv/oss.c
@@ -70,6 +70,24 @@ static int muldiv( int a, int b, int c )
     return ret;
 }
 
+static void oss_lock(struct oss_stream *stream)
+{
+    pthread_mutex_lock(&stream->lock);
+}
+
+static void oss_unlock(struct oss_stream *stream)
+{
+    pthread_mutex_unlock(&stream->lock);
+}
+
+static NTSTATUS oss_unlock_result(struct oss_stream *stream,
+                                  HRESULT *result, HRESULT value)
+{
+    *result = value;
+    oss_unlock(stream);
+    return STATUS_SUCCESS;
+}
+
 static NTSTATUS test_connect(void *args)
 {
     struct test_connect_params *params = args;
@@ -732,6 +750,18 @@ static NTSTATUS get_mix_format(void *args)
     return STATUS_SUCCESS;
 }
 
+static NTSTATUS get_buffer_size(void *args)
+{
+    struct get_buffer_size_params *params = args;
+    struct oss_stream *stream = params->stream;
+
+    oss_lock(stream);
+
+    *params->size = stream->bufsize_frames;
+
+    return oss_unlock_result(stream, &params->result, S_OK);
+}
+
 unixlib_entry_t __wine_unix_call_funcs[] =
 {
     test_connect,
@@ -740,4 +770,5 @@ unixlib_entry_t __wine_unix_call_funcs[] =
     release_stream,
     is_format_supported,
     get_mix_format,
+    get_buffer_size,
 };
diff --git a/dlls/wineoss.drv/unixlib.h b/dlls/wineoss.drv/unixlib.h
index c0a0b25c374..b57798ef435 100644
--- a/dlls/wineoss.drv/unixlib.h
+++ b/dlls/wineoss.drv/unixlib.h
@@ -106,6 +106,13 @@ struct get_mix_format_params
     HRESULT result;
 };
 
+struct get_buffer_size_params
+{
+    struct oss_stream *stream;
+    HRESULT result;
+    UINT32 *size;
+};
+
 enum oss_funcs
 {
     oss_test_connect,
@@ -114,6 +121,7 @@ enum oss_funcs
     oss_release_stream,
     oss_is_format_supported,
     oss_get_mix_format,
+    oss_get_buffer_size,
 };
 
 extern unixlib_handle_t oss_handle;