diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 9fdadbb74f3..c140a7e43ce 100644
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -1091,11 +1091,15 @@ Value Eval::evaluate(const Position& pos) {
       v = Evaluation<NO_TRACE>(pos).value();          // classical
   else
   {
-      int scale =   898
-                  + 24 * pos.count<PAWN>()
-                  + 33 * pos.non_pawn_material() / 1024;
+       int scale =   898
+                   + 24 * pos.count<PAWN>()
+                   + 33 * pos.non_pawn_material() / 1024;
 
-       v = NNUE::evaluate(pos, true) * scale / 1024;  // NNUE
+       Value nnue     = NNUE::evaluate(pos, true);     // NNUE
+       Color stm      = pos.side_to_move();
+       Value optimism = pos.this_thread()->optimism[stm];
+
+       v = (nnue + optimism) * scale / 1024 - optimism;
 
        if (pos.is_chess960())
            v += fix_FRC(pos);
diff --git a/src/misc.h b/src/misc.h
index 718e5558178..f75e7e4e74f 100644
--- a/src/misc.h
+++ b/src/misc.h
@@ -138,6 +138,33 @@ class ValueList {
   std::size_t size_ = 0;
 };
 
+
+/// sigmoid(t, x0, y0, C, P, Q) implements a sigmoid-like function
+/// using only integers, with the following properties:
+/// 
+///  -  sigmoid is centered in (x0, y0)
+///  -  sigmoid has amplitude [-P/Q , P/Q] instead of [-1 , +1]
+///  -  limit is (y0 - P/Q) when t tends to -infinity
+///  -  limit is (y0 + P/Q) when t tends to +infinity
+///  -  the slope can be adjusted using C > 0, smaller C giving a steeper sigmoid
+///  -  the slope of the sigmoid when t = x0 is P/(Q*C)
+///  -  sigmoid is increasing with t when P > 0 and Q > 0
+///  -  to get a decreasing sigmoid, call with -t, or change sign of P
+///  -  mean value of the sigmoid is y0
+///
+/// Use <https://www.desmos.com/calculator/jhh83sqq92> to draw the sigmoid
+
+inline int64_t sigmoid(int64_t t, int64_t x0,
+                                  int64_t y0,
+                                  int64_t  C,
+                                  int64_t  P,
+                                  int64_t  Q)
+{
+   assert(C > 0);
+   return y0 + P * (t-x0) / (Q * (std::abs(t-x0) + C)) ;
+}
+
+
 /// xorshift64star Pseudo-Random Number Generator
 /// This class is based on original code written and dedicated
 /// to the public domain by Sebastiano Vigna (2014).
diff --git a/src/search.cpp b/src/search.cpp
index fabb0ff07ac..fa2f506bc1e 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -334,8 +334,10 @@ void Thread::search() {
 
   nodesLastExplosive = nodes;
   nodesLastNormal    = nodes;
-  state = EXPLOSION_NONE;
-  trend = SCORE_ZERO;
+  state              = EXPLOSION_NONE;
+  trend              = SCORE_ZERO;
+  optimism[ us]      = Value(25);
+  optimism[~us]      = -optimism[us];
 
   int searchAgainCounter = 0;
 
@@ -381,11 +383,14 @@ void Thread::search() {
               alpha = std::max(prev - delta,-VALUE_INFINITE);
               beta  = std::min(prev + delta, VALUE_INFINITE);
 
-              // Adjust trend based on root move's previousScore (dynamic contempt)
-              int tr = 113 * prev / (abs(prev) + 147);
-
+              // Adjust trend and optimism based on root move's previousScore
+              int tr = sigmoid(prev, 0, 0, 147, 113, 1);
               trend = (us == WHITE ?  make_score(tr, tr / 2)
                                    : -make_score(tr, tr / 2));
+
+              int opt = sigmoid(prev, 0, 25, 147, 113, 2);
+              optimism[ us] = Value(opt);
+              optimism[~us] = -optimism[us];
           }
 
           // Start with a small aspiration window and, in the case of a fail
diff --git a/src/thread.h b/src/thread.h
index 387937390c1..cd206faab98 100644
--- a/src/thread.h
+++ b/src/thread.h
@@ -68,6 +68,7 @@ class Thread {
   int selDepth, nmpMinPly;
   Color nmpColor;
   ExplosionState state;
+  Value optimism[COLOR_NB];
 
   Position rootPos;
   StateInfo rootState;