diff --git a/dix/ptrveloc.c b/dix/ptrveloc.c
index b6d2daefe..d6fef9cf3 100644
--- a/dix/ptrveloc.c
+++ b/dix/ptrveloc.c
@@ -77,7 +77,7 @@ DeletePredictableAccelerationProperties(DeviceIntPtr,
 /*#define PTRACCEL_DEBUGGING*/
 
 #ifdef PTRACCEL_DEBUGGING
-#define DebugAccelF ErrorFSigSafe
+#define DebugAccelF(...) ErrorFSigSafe("dix/ptraccel: " __VA_ARGS__)
 #else
 #define DebugAccelF(...)        /* */
 #endif
@@ -421,7 +421,7 @@ void
 InitTrackers(DeviceVelocityPtr vel, int ntracker)
 {
     if (ntracker < 1) {
-        ErrorF("(dix ptracc) invalid number of trackers\n");
+        ErrorF("invalid number of trackers\n");
         return;
     }
     free(vel->tracker);
@@ -566,7 +566,7 @@ FeedTrackers(DeviceVelocityPtr vel, double dx, double dy, int cur_t)
     vel->tracker[n].dy = 0.0;
     vel->tracker[n].time = cur_t;
     vel->tracker[n].dir = GetDirection(dx, dy);
-    DebugAccelF("(dix prtacc) motion [dx: %f dy: %f dir:%d diff: %d]\n",
+    DebugAccelF("motion [dx: %f dy: %f dir:%d diff: %d]\n",
                 dx, dy, vel->tracker[n].dir,
                 cur_t - vel->tracker[vel->cur_tracker].time);
     vel->cur_tracker = n;
@@ -614,7 +614,7 @@ QueryTrackers(DeviceVelocityPtr vel, int cur_t)
 
         /* bail out if data is too old and protect from overrun */
         if (age_ms >= vel->reset_time || age_ms < 0) {
-            DebugAccelF("(dix prtacc) query: tracker too old (reset after %d, age is %d)\n",
+            DebugAccelF("query: tracker too old (reset after %d, age is %d)\n",
                         vel->reset_time, age_ms);
             break;
         }
@@ -627,7 +627,7 @@ QueryTrackers(DeviceVelocityPtr vel, int cur_t)
          */
         dir &= tracker->dir;
         if (dir == 0) {         /* we've changed octant of movement (e.g. NE → NW) */
-            DebugAccelF("(dix prtacc) query: no longer linear\n");
+            DebugAccelF("query: no longer linear\n");
             /* instead of breaking it we might also inspect the partition after,
              * but actual improvement with this is probably rare. */
             break;
@@ -648,7 +648,7 @@ QueryTrackers(DeviceVelocityPtr vel, int cur_t)
                 velocity_diff / (initial_velocity + tracker_velocity) >=
                 vel->max_rel_diff) {
                 /* we're not in range, quit - it won't get better. */
-                DebugAccelF("(dix prtacc) query: tracker too different:"
+                DebugAccelF("query: tracker too different:"
                             " old %2.2f initial %2.2f diff: %2.2f\n",
                             tracker_velocity, initial_velocity, velocity_diff);
                 break;
@@ -661,14 +661,14 @@ QueryTrackers(DeviceVelocityPtr vel, int cur_t)
         }
     }
     if (offset == vel->num_tracker) {
-        DebugAccelF("(dix prtacc) query: last tracker in effect\n");
+        DebugAccelF("query: last tracker in effect\n");
         used_offset = vel->num_tracker - 1;
     }
     if (used_offset >= 0) {
 #ifdef PTRACCEL_DEBUGGING
         MotionTracker *tracker = TRACKER(vel, used_offset);
 
-        DebugAccelF("(dix prtacc) result: offset %i [dx: %f dy: %f diff: %i]\n",
+        DebugAccelF("result: offset %i [dx: %f dy: %f diff: %i]\n",
                     used_offset, tracker->dx, tracker->dy,
                     cur_t - tracker->time);
 #endif
@@ -694,6 +694,8 @@ ProcessVelocityData2D(DeviceVelocityPtr vel, double dx, double dy, int time)
 
     velocity = QueryTrackers(vel, time);
 
+    DebugAccelF("velocity is %f\n", velocity);
+
     vel->velocity = velocity;
     return velocity == 0;
 }
@@ -769,7 +771,7 @@ ComputeAcceleration(DeviceIntPtr dev,
     double result;
 
     if (vel->velocity <= 0) {
-        DebugAccelF("(dix ptracc) profile skipped\n");
+        DebugAccelF("profile skipped\n");
         /*
          * If we have no idea about device velocity, don't pretend it.
          */
@@ -793,13 +795,13 @@ ComputeAcceleration(DeviceIntPtr dev,
                                             threshold,
                                             acc);
         result /= 6.0f;
-        DebugAccelF("(dix ptracc) profile average [%.2f ... %.2f] is %.3f\n",
+        DebugAccelF("profile average [%.2f ... %.2f] is %.3f\n",
                     vel->velocity, vel->last_velocity, result);
     }
     else {
         result = BasicComputeAcceleration(dev, vel,
                                           vel->velocity, threshold, acc);
-        DebugAccelF("(dix ptracc) profile sample [%.2f] is %.3f\n",
+        DebugAccelF("profile sample [%.2f] is %.3f\n",
                     vel->velocity, result);
     }
 
@@ -1111,6 +1113,7 @@ acceleratePointerPredictable(DeviceIntPtr dev, ValuatorMask *val, CARD32 evtime)
                                        (double) dev->ptrfeed->ctrl.num /
                                        (double) dev->ptrfeed->ctrl.den);
 
+            DebugAccelF("mult is %f\n", mult);
             if (mult != 1.0f || velocitydata->const_acceleration != 1.0f) {
                 if (mult > 1.0f && soften)
                     ApplySoftening(velocitydata, &dx, &dy);