diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 1c30a5ac..c0c7e5ff 100644
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -396,10 +396,9 @@ namespace {
             // Penalty when trapped by the king, even more if the king cannot castle
             else if (mob <= 3)
             {
-                Square ksq = pos.square<KING>(Us);
+                File kf = file_of(pos.square<KING>(Us));
 
-                if (   ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
-                    && !pe->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
+                if ((kf < FILE_E) == (file_of(s) < kf))
                     score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
             }
         }
diff --git a/src/pawns.h b/src/pawns.h
index a9c21ffb..669999bf 100644
--- a/src/pawns.h
+++ b/src/pawns.h
@@ -45,10 +45,6 @@ struct Entry {
     return semiopenFiles[c] & (1 << f);
   }
 
-  int semiopen_side(Color c, File f, bool leftSide) const {
-    return semiopenFiles[c] & (leftSide ? (1 << f) - 1 : ~((1 << (f + 1)) - 1));
-  }
-
   int pawns_on_same_color_squares(Color c, Square s) const {
     return pawnsOnSquares[c][bool(DarkSquares & s)];
   }