diff --git a/src/loader/loader_dri3_helper.c b/src/loader/loader_dri3_helper.c
index 2eef6e6..68febcc 100644
--- a/src/loader/loader_dri3_helper.c
+++ b/src/loader/loader_dri3_helper.c
@@ -32,7 +32,6 @@
 
 #include <X11/Xlib-xcb.h>
 
-#include <c11/threads.h>
 #include "loader_dri3_helper.h"
 
 /* From xmlpool/options.h, user exposed so should be stable */
@@ -261,6 +260,7 @@ loader_dri3_drawable_init(xcb_connection_t *conn,
    GLint vblank_mode = DRI_CONF_VBLANK_DEF_INTERVAL_1;
    int swap_interval;
 
+   mtx_init(&draw->mtx, mtx_recursive);
    draw->conn = conn;
    draw->ext = ext;
    draw->vtable = vtable;
@@ -467,23 +467,30 @@ loader_dri3_wait_for_sbc(struct loader_dri3_drawable *draw,
                          int64_t target_sbc, int64_t *ust,
                          int64_t *msc, int64_t *sbc)
 {
+
+   mtx_lock(&draw->mtx);
+
    /* From the GLX_OML_sync_control spec:
     *
     *     "If <target_sbc> = 0, the function will block until all previous
-    *      swaps requested with glXSwapBuffersMscOML for that window have
+    *      swaps requested with glXSwapBuffersMscOML for thatq window have
     *      completed."
     */
    if (!target_sbc)
       target_sbc = draw->send_sbc;
 
    while (draw->recv_sbc < target_sbc) {
-      if (!dri3_wait_for_event(draw))
+      if (!dri3_wait_for_event(draw)) {
+         mtx_unlock(&draw->mtx);
          return 0;
+      }
    }
 
    *ust = draw->ust;
    *msc = draw->msc;
    *sbc = draw->recv_sbc;
+
+   mtx_unlock(&draw->mtx);
    return 1;
 }
 
@@ -769,7 +776,9 @@ loader_dri3_swap_buffers_msc(struct loader_dri3_drawable *draw,
    int64_t ret = 0;
    uint32_t options = XCB_PRESENT_OPTION_NONE;
    int swap_interval;
+   uint64_t send_sbc;
 
+   mtx_lock(&draw->mtx);
    swap_interval = draw->vtable->get_swap_interval(draw);
 
    draw->vtable->flush_drawable(draw, flush_flags);
@@ -816,10 +825,10 @@ loader_dri3_swap_buffers_msc(struct loader_dri3_drawable *draw,
        * request. target_msc=divisor=remainder=0 means "Use glXSwapBuffers()
        * semantic"
        */
-      ++draw->send_sbc;
+      send_sbc = draw->send_sbc + 1;
       if (target_msc == 0 && divisor == 0 && remainder == 0)
          target_msc = draw->msc + swap_interval *
-                      (draw->send_sbc - draw->recv_sbc);
+                      (send_sbc - draw->recv_sbc);
       else if (divisor == 0 && remainder > 0) {
          /* From the GLX_OML_sync_control spec:
           *     "If <divisor> = 0, the swap will occur when MSC becomes
@@ -853,11 +862,11 @@ loader_dri3_swap_buffers_msc(struct loader_dri3_drawable *draw,
          options |= XCB_PRESENT_OPTION_COPY;
 
       back->busy = 1;
-      back->last_swap = draw->send_sbc;
+      back->last_swap = send_sbc;
       xcb_present_pixmap(draw->conn,
                          draw->drawable,
                          back->pixmap,
-                         (uint32_t) draw->send_sbc,
+                         (uint32_t) send_sbc,
                          0,                                    /* valid */
                          0,                                    /* update */
                          0,                                    /* x_off */
@@ -869,7 +878,7 @@ loader_dri3_swap_buffers_msc(struct loader_dri3_drawable *draw,
                          target_msc,
                          divisor,
                          remainder, 0, NULL);
-      ret = (int64_t) draw->send_sbc;
+      ret = (int64_t) send_sbc;
 
       /* Schedule a server-side back-preserving blit if necessary.
        * This happens iff all conditions below are satisfied:
@@ -892,12 +901,14 @@ loader_dri3_swap_buffers_msc(struct loader_dri3_drawable *draw,
       }
 
       xcb_flush(draw->conn);
+      draw->send_sbc = send_sbc;
       if (draw->stamp)
          ++(*draw->stamp);
    }
 
    draw->ext->flush->invalidate(draw->dri_drawable);
 
+   mtx_unlock(&draw->mtx);
    return ret;
 }
 
diff --git a/src/loader/loader_dri3_helper.h b/src/loader/loader_dri3_helper.h
index 7af94bd..ae4db86 100644
--- a/src/loader/loader_dri3_helper.h
+++ b/src/loader/loader_dri3_helper.h
@@ -33,6 +33,7 @@
 
 #include <GL/gl.h>
 #include <GL/internal/dri_interface.h>
+#include <c11/threads.h>
 
 enum loader_dri3_buffer_type {
    loader_dri3_buffer_back = 0,
@@ -161,6 +162,8 @@ struct loader_dri3_drawable {
 
    unsigned int swap_method;
    unsigned int back_format;
+
+   mtx_t mtx;
 };
 
 void