diff --git a/encoder/ratecontrol.c b/encoder/ratecontrol.c
index a049f74..557b920 100644
--- a/encoder/ratecontrol.c
+++ b/encoder/ratecontrol.c
@@ -1467,10 +1467,15 @@ static float rate_estimate_qscale( x264_t *h )
         if( rcc->b_2pass )
         {
             //FIXME adjust abr_buffer based on distance to the end of the video
-            int64_t diff = total_bits - (int64_t)rce.expected_bits;
+            int64_t diff;
+
+            if( h->fenc->i_frame < h->param.i_threads )
+                diff = total_bits + (int64_t)h->fenc->i_frame * rcc->bitrate / rcc->fps - (int64_t)rce.expected_bits;
+            else
+                diff = total_bits + (int64_t)(h->param.i_threads - 1) * rcc->bitrate / rcc->fps - (int64_t)rce.expected_bits;
             q = rce.new_qscale;
             q /= x264_clip3f((double)(abr_buffer - diff) / abr_buffer, .5, 2);
-            if( h->fenc->i_frame > 30 )
+            if( h->fenc->i_frame + 1 - h->param.i_threads >= rcc->fps && rcc->expected_bits_sum > 0)
             {
                 /* Adjust quant based on the difference between
                  * achieved and expected bitrate so far */
@@ -1542,7 +1547,7 @@ static float rate_estimate_qscale( x264_t *h )
                 wanted_bits = i_frame_done * rcc->bitrate / rcc->fps;
                 if( wanted_bits > 0 )
                 {
-                    abr_buffer *= X264_MAX( 1, sqrt(i_frame_done/25) );
+                    abr_buffer *= X264_MAX( 1, sqrt(i_frame_done / rcc->fps) );
                     overflow = x264_clip3f( 1.0 + (total_bits - wanted_bits) / abr_buffer, .5, 2 );
                     q *= overflow;
                 }