diff --git classify/trainingsampleset.cpp classify/trainingsampleset.cpp
index afbf3f4..6121395 100644
--- classify/trainingsampleset.cpp
+++ classify/trainingsampleset.cpp
@@ -693,6 +693,8 @@ void TrainingSampleSet::ComputeCanonicalSamples(const IntFeatureMap& map,
       fcinfo.canonical_sample = fcinfo.samples[0];
       fcinfo.canonical_dist = 0.0f;
       for (int i = 0; i < fcinfo.samples.size(); ++i) {
+        #pragma omp parallel
+        {
         int s1 = fcinfo.samples[i];
         const GenericVector<int>& features1 = samples_[s1]->indexed_features();
         f_table.Set(features1, features1.size(), true);
@@ -701,6 +703,7 @@ void TrainingSampleSet::ComputeCanonicalSamples(const IntFeatureMap& map,
         // reasonably fast because f_table.FeatureDistance is fast, but we
         // may have to reconsider if we start playing with too many samples
         // of a single char/font.
+        #pragma omp for
         for (int j = 0; j < fcinfo.samples.size(); ++j) {
           int s2 = fcinfo.samples[j];
           if (samples_[s2]->class_id() != c  ||
@@ -709,11 +712,14 @@ void TrainingSampleSet::ComputeCanonicalSamples(const IntFeatureMap& map,
             continue;
           GenericVector<int> features2 = samples_[s2]->indexed_features();
           double dist = f_table.FeatureDistance(features2);
-          if (dist > max_dist) {
-            max_dist = dist;
-            if (dist > max_max_dist) {
-              max_s1 = s1;
-              max_s2 = s2;
+          #pragma omp critical(inner_comparison)
+          {
+            if (dist > max_dist) {
+              max_dist = dist;
+              if (dist > max_max_dist) {
+                max_s1 = s1;
+                max_s2 = s2;
+              }
             }
           }
         }
@@ -727,6 +733,7 @@ void TrainingSampleSet::ComputeCanonicalSamples(const IntFeatureMap& map,
           fcinfo.canonical_dist = max_dist;
         }
         UpdateRange(max_dist, &min_max_dist, &max_max_dist);
+        }
       }
       if (max_max_dist > global_worst_dist) {
         // Keep a record of the worst pair over all characters/fonts too.