diff --git a/src/evergreen_accel.c b/src/evergreen_accel.c
index 5c95e20..47f3edc 100644
--- a/src/evergreen_accel.c
+++ b/src/evergreen_accel.c
@@ -284,9 +284,6 @@ void evergreen_cp_wait_vline_sync(ScrnInfoPtr pScrn, PixmapPtr pPix,
 
     drmmode_crtc = crtc->driver_private;
 
-    if (stop < start)
-        return;
-
     if (!crtc->enabled)
         return;
 
@@ -306,16 +303,12 @@ void evergreen_cp_wait_vline_sync(ScrnInfoPtr pScrn, PixmapPtr pPix,
 	    return;
     }
 
-    start = max(start, 0);
-    stop = min(stop, crtc->mode.VDisplay);
+    start = max(start, crtc->y);
+    stop = min(stop, crtc->y + crtc->mode.VDisplay);
 
-    if (start > crtc->mode.VDisplay)
+    if (stop <= start)
         return;
 
-    /* on r5xx+ vline starts at viewport_y */
-    start += crtc->y;
-    stop += crtc->y;
-
     BEGIN_BATCH(11);
     /* set the VLINE range */
     EREG(EVERGREEN_VLINE_START_END, /* this is just a marker */
diff --git a/src/r6xx_accel.c b/src/r6xx_accel.c
index 752165b..2683de9 100644
--- a/src/r6xx_accel.c
+++ b/src/r6xx_accel.c
@@ -345,9 +345,6 @@ r600_cp_wait_vline_sync(ScrnInfoPtr pScrn, drmBufPtr ib, PixmapPtr pPix,
     if (!crtc)
         return;
 
-    if (stop < start)
-        return;
-
     if (!crtc->enabled)
         return;
 
@@ -367,16 +364,14 @@ r600_cp_wait_vline_sync(ScrnInfoPtr pScrn, drmBufPtr ib, PixmapPtr pPix,
 	    return;
     }
 
-    start = max(start, 0);
-    stop = min(stop, crtc->mode.VDisplay);
+    ErrorF("(start, stop) before clamping: (%d, %d)\n", start, stop);
+    start = max(start, crtc->y);
+    stop = min(stop, crtc->y + crtc->mode.VDisplay);
+    ErrorF("(start, stop) after clamping: (%d, %d)\n", start, stop);
 
-    if (start > crtc->mode.VDisplay)
+    if (stop <= start)
         return;
 
-    /* on r5xx+ vline starts at viewport_y */
-    start += crtc->y;
-    stop += crtc->y;
-
 #if defined(XF86DRM_MODE)
     if (info->cs) {
 	drmmode_crtc_private_ptr drmmode_crtc = crtc->driver_private;
diff --git a/src/radeon_commonfuncs.c b/src/radeon_commonfuncs.c
index d399257..18ae67b 100644
--- a/src/radeon_commonfuncs.c
+++ b/src/radeon_commonfuncs.c
@@ -905,9 +905,6 @@ void FUNC_NAME(RADEONWaitForVLine)(ScrnInfoPtr pScrn, PixmapPtr pPix,
     if (!crtc)
 	return;
 
-    if (stop < start)
-	return;
-
     if (!crtc->enabled)
 	return;
 
@@ -927,16 +924,16 @@ void FUNC_NAME(RADEONWaitForVLine)(ScrnInfoPtr pScrn, PixmapPtr pPix,
 	    return;
     }
 
-    start = max(start, 0);
-    stop = min(stop, crtc->mode.VDisplay);
+    start = max(start, crtc->y);
+    stop = min(stop, crtc->y + crtc->mode.VDisplay);
 
-    if (start > crtc->mode.VDisplay)
+    if (stop <= start)
 	return;
 
-    if (IS_AVIVO_VARIANT) {
-	/* on r5xx+ vline starts at viewport_y */
-	start += crtc->y;
-	stop += crtc->y;
+    if (!IS_AVIVO_VARIANT) {
+	/* on pre-r5xx vline starts at CRTC scanout */
+	start -= crtc->y;
+	stop -= crtc->y;
     }
 
 #if defined(ACCEL_CP) && defined(XF86DRM_MODE)