diff --git a/engine/src/generate.cpp b/engine/src/generate.cpp
index de0cbc667..b96f86c7e 100644
--- a/engine/src/generate.cpp
+++ b/engine/src/generate.cpp
@@ -281,7 +281,7 @@ namespace wisdom
             appendMove (knight_move);
     }
 
-    auto 
+    auto
     eligibleEnPassantColumn (const Board& board, int row, int column, Color who)
         -> optional<int>
     {
@@ -581,4 +581,19 @@ namespace wisdom
         return non_checks;
     }
 
+    auto
+    needPawnPromotion (int row, Color who)
+        -> bool
+    {
+        assert (isColorValid (who));
+        switch (who)
+        {
+            case Color::White:
+                return 0 == row;
+            case Color::Black:
+                return 7 == row;
+            default:
+                throw Error { "Invalid color in needPawnPromotion()" };
+        }
+    }
 }
diff --git a/engine/src/generate.hpp b/engine/src/generate.hpp
index 2bdfe185e..4911e5fc5 100644
--- a/engine/src/generate.hpp
+++ b/engine/src/generate.hpp
@@ -15,21 +15,9 @@ namespace wisdom
     generateLegalMoves (const Board& board, Color who)
         -> MoveList;
 
-    [[nodiscard]] inline auto 
+    [[nodiscard]] auto
     needPawnPromotion (int row, Color who) 
-        -> bool
-    {
-        assert (isColorValid (who));
-        switch (who)
-        {
-            case Color::White:
-                return 0 == row;
-            case Color::Black:
-                return 7 == row;
-            default:
-                throw Error { "Invalid color in needPawnPromotion()" };
-        }
-    }
+        -> bool;
 
     // Return en passant column if the board is the player is eligible.
     [[nodiscard]] auto