diff --git a/USolver.pas b/USolver.pas
index 53aea0d..5eacddf 100644
--- a/USolver.pas
+++ b/USolver.pas
@@ -63,9 +63,9 @@ type
 
   TSolverEngine = class
   public
-    procedure ProcessData(constref ASolver: ISolver);
-    procedure Run(constref ASolver: ISolver);
-    procedure RunAndFree(constref ASolver: ISolver);
+    procedure ProcessData(const ASolver: ISolver);
+    procedure Run(const ASolver: ISolver);
+    procedure RunAndFree(const ASolver: ISolver);
   end;
 
 implementation
@@ -90,7 +90,7 @@ end;
 
 { TSolverEngine }
 
-procedure TSolverEngine.ProcessData(constref ASolver: ISolver);
+procedure TSolverEngine.ProcessData(const ASolver: ISolver);
 var
   data: TextFile;
   s: string;
@@ -112,7 +112,7 @@ begin
   ASolver.Finish;
 end;
 
-procedure TSolverEngine.Run(constref ASolver: ISolver);
+procedure TSolverEngine.Run(const ASolver: ISolver);
 begin
   WriteLn;
   WriteLn('--- ', ASolver.PuzzleName, ' ---');
@@ -121,7 +121,7 @@ begin
   WriteLn('Part 2: ', ASolver.ResultPart2);
 end;
 
-procedure TSolverEngine.RunAndFree(constref ASolver: ISolver);
+procedure TSolverEngine.RunAndFree(const ASolver: ISolver);
 begin
   Run(ASolver);
   ASolver.Free;