diff --git a/latin.c b/latin.c
index 34c06c4..116cdae 100644
--- a/latin.c
+++ b/latin.c
@@ -16,6 +16,10 @@
  * Solver.
  */
 
+#ifdef STANDALONE_SOLVER
+int solver_show_working, solver_recurse_depth;
+#endif
+
 /*
  * Function called when we are certain that a particular square has
  * a particular number in it. The y-coordinate passed in here is
diff --git a/latin.h b/latin.h
index dbea6e4..4ec6954 100644
--- a/latin.h
+++ b/latin.h
@@ -8,7 +8,7 @@ typedef unsigned char digit;
 /* --- Solver structures, definitions --- */
 
 #ifdef STANDALONE_SOLVER
-int solver_show_working, solver_recurse_depth;
+extern int solver_show_working, solver_recurse_depth;
 #endif
 
 struct latin_solver {