diff --git a/src/enc/histogram.c b/src/enc/histogram.c
index dbc102ab..c5b84bf7 100644
--- a/src/enc/histogram.c
+++ b/src/enc/histogram.c
@@ -249,8 +249,7 @@ static uint32_t MyRand(uint32_t *seed) {
 }
 
 static int HistogramCombine(const VP8LHistogramSet* const in,
-                            VP8LHistogramSet* const out,
-                            int min_cluster_size, int iter_mult,
+                            VP8LHistogramSet* const out, int iter_mult,
                             int num_pairs, int num_tries_no_success) {
   int ok = 0;
   int i, iter;
@@ -258,6 +257,7 @@ static int HistogramCombine(const VP8LHistogramSet* const in,
   int tries_with_no_success = 0;
   int out_size = in->size;
   const int outer_iters = in->size * iter_mult;
+  const int min_cluster_size = 2;
   VP8LHistogram* const histos = (VP8LHistogram*)malloc(2 * sizeof(*histos));
   VP8LHistogram* cur_combo = histos + 0;    // trial merged histogram
   VP8LHistogram* best_combo = histos + 1;   // best merged histogram so far
@@ -272,12 +272,12 @@ static int HistogramCombine(const VP8LHistogramSet* const in,
 
   // Collapse similar histograms in 'out'.
   for (iter = 0; iter < outer_iters && out_size >= min_cluster_size; ++iter) {
-    // We pick the best pair to be combined out of 'inner_iters' pairs.
     double best_cost_diff = 0.;
     int best_idx1 = 0, best_idx2 = 1;
     int j;
+    const int num_tries = (num_pairs < out_size) ? num_pairs : out_size;
     seed += iter;
-    for (j = 0; j < num_pairs; ++j) {
+    for (j = 0; j < num_tries; ++j) {
       double curr_cost_diff;
       // Choose two histograms at random and try to combine them.
       const uint32_t idx1 = MyRand(&seed) % out_size;
@@ -386,21 +386,26 @@ int VP8LGetHistoImageSymbols(int xsize, int ysize,
   const int histo_xsize = histo_bits ? VP8LSubSampleSize(xsize, histo_bits) : 1;
   const int histo_ysize = histo_bits ? VP8LSubSampleSize(ysize, histo_bits) : 1;
   const int histo_image_raw_size = histo_xsize * histo_ysize;
+
   // Heuristic params for HistogramCombine().
-  const int num_pairs = 8 + (quality >> 1);
   const int num_tries_no_success = 8 + (quality >> 1);
-  const int min_cluster_size = (quality >= 25) ? ((quality >= 75) ? 2 : 3) : 4;
-  const int iter_mult = (quality >= 25) ? ((quality >= 75) ? 3 : 2) : 1;
+  const int iter_mult = (quality < 27) ? 1 : 1 + ((quality - 27) >> 4);
+  int num_pairs = (quality >> 1);
 
   VP8LHistogramSet* const image_out =
       VP8LAllocateHistogramSet(histo_image_raw_size, cache_bits);
   if (image_out == NULL) return 0;
 
+  if (num_pairs > (histo_image_raw_size >> 2)) {
+    num_pairs = histo_image_raw_size >> 2;
+  }
+  num_pairs += 10;
+
   // Build histogram image.
   HistogramBuildImage(xsize, histo_bits, refs, image_out);
   // Collapse similar histograms.
-  if (!HistogramCombine(image_out, image_in, min_cluster_size, iter_mult,
-                        num_pairs, num_tries_no_success)) {
+  if (!HistogramCombine(image_out, image_in, iter_mult, num_pairs,
+                        num_tries_no_success)) {
     goto Error;
   }
   // Find the optimal map from original histograms to the final ones.