diff --git a/gdk/gdkframeclock.c b/gdk/gdkframeclock.c
index 00a1631c13..9c3d4238cb 100644
--- a/gdk/gdkframeclock.c
+++ b/gdk/gdkframeclock.c
@@ -269,7 +269,7 @@ gdk_frame_clock_init (GdkFrameClock *clock)
  * Return value: a timestamp in microseconds, in the timescale of
  *  of g_get_monotonic_time().
  */
-guint64
+gint64
 gdk_frame_clock_get_frame_time (GdkFrameClock *frame_clock)
 {
   g_return_val_if_fail (GDK_IS_FRAME_CLOCK (frame_clock), 0);
diff --git a/gdk/gdkframeclock.h b/gdk/gdkframeclock.h
index 2459708d01..7b011caa25 100644
--- a/gdk/gdkframeclock.h
+++ b/gdk/gdkframeclock.h
@@ -76,7 +76,7 @@ typedef enum {
 
 GType    gdk_frame_clock_get_type             (void) G_GNUC_CONST;
 
-guint64  gdk_frame_clock_get_frame_time            (GdkFrameClock *frame_clock);
+gint64   gdk_frame_clock_get_frame_time            (GdkFrameClock *frame_clock);
 
 GDK_AVAILABLE_IN_3_8
 void               gdk_frame_clock_request_phase (GdkFrameClock      *frame_clock,
diff --git a/gdk/gdkframeclockidle.c b/gdk/gdkframeclockidle.c
index 5974e269ea..5e751b3d92 100644
--- a/gdk/gdkframeclockidle.c
+++ b/gdk/gdkframeclockidle.c
@@ -37,9 +37,9 @@ struct _GdkFrameClockIdlePrivate
 {
   GTimer *timer;
   /* timer_base is used to avoid ever going backward */
-  guint64 timer_base;
-  guint64 frame_time;
-  guint64 min_next_frame_time;
+  gint64 timer_base;
+  gint64 frame_time;
+  gint64 min_next_frame_time;
   gint64 sleep_serial;
 
   guint flush_idle_id;
@@ -135,12 +135,12 @@ gdk_frame_clock_idle_finalize (GObject *object)
   G_OBJECT_CLASS (gdk_frame_clock_idle_parent_class)->finalize (object);
 }
 
-static guint64
+static gint64
 compute_frame_time (GdkFrameClockIdle *idle)
 {
   GdkFrameClockIdlePrivate *priv = idle->priv;
-  guint64 computed_frame_time;
-  guint64 elapsed;
+  gint64 computed_frame_time;
+  gint64 elapsed;
 
   elapsed = g_get_monotonic_time () + priv->timer_base;
   if (elapsed < priv->frame_time)
@@ -160,11 +160,11 @@ compute_frame_time (GdkFrameClockIdle *idle)
   return computed_frame_time;
 }
 
-static guint64
+static gint64
 gdk_frame_clock_idle_get_frame_time (GdkFrameClock *clock)
 {
   GdkFrameClockIdlePrivate *priv = GDK_FRAME_CLOCK_IDLE (clock)->priv;
-  guint64 computed_frame_time;
+  gint64 computed_frame_time;
 
   /* can't change frame time during a paint */
   if (priv->phase != GDK_FRAME_CLOCK_PHASE_NONE &&
@@ -196,8 +196,8 @@ maybe_start_idle (GdkFrameClockIdle *clock_idle)
 
       if (priv->min_next_frame_time != 0)
         {
-          guint64 now = compute_frame_time (clock_idle);
-          guint64 min_interval_us = MAX (priv->min_next_frame_time, now) - now;
+          gint64 now = compute_frame_time (clock_idle);
+          gint64 min_interval_us = MAX (priv->min_next_frame_time, now) - now;
           min_interval = (min_interval_us + 500) / 1000;
         }
 
diff --git a/gdk/gdkframeclockprivate.h b/gdk/gdkframeclockprivate.h
index 262b32746b..0ce74da23e 100644
--- a/gdk/gdkframeclockprivate.h
+++ b/gdk/gdkframeclockprivate.h
@@ -47,7 +47,7 @@ struct _GdkFrameClockClass
 {
   GObjectClass parent_class;
 
-  guint64  (* get_frame_time) (GdkFrameClock *clock);
+  gint64   (* get_frame_time) (GdkFrameClock *clock);
 
   void     (* request_phase)  (GdkFrameClock      *clock,
                                GdkFrameClockPhase  phase);