diff --git a/assembler.pas b/assembler.pas
index f226dd0..b647db3 100644
--- a/assembler.pas
+++ b/assembler.pas
@@ -48,28 +48,28 @@ end;
 procedure LblError;
 begin
     writeln ('Error (line ', LP, '): illegal label');
-    halt;
+    halt (1);
 end;
 
 //Print a reference error and abort
 procedure RefError;
 begin
     writeln ('Error (line ', LP, '): illegal reference(s) relative to this line');
-    halt;
+    halt (1);
 end;
 
 //Print an argument error and abort
 procedure ArgError;
 begin
     writeln ('Error (line ', LP, '): illegal argument(s)');
-    halt;
+    halt (1);
 end;
 
 //Print a memory error and abort if the assembler is about to write beyond available memory
 procedure MemError;
 begin
     writeln ('Error (line ', LP, '): memory overflow');
-    halt;
+    halt (1);
 end;
 
 //Assemble a single register argument
@@ -163,7 +163,7 @@ begin
     //Check for and set up a program file
     if ParamCount <> 1 then begin
         writeln ('Usage: assembler program (< input)');
-        halt;
+        halt (1);
     end;
 
     //Initialise the byte and start pointers
@@ -259,7 +259,7 @@ begin
                 end
                 else begin
                     writeln ('Error (line ', LP, '): ORG must be the first instruction');
-                    halt;
+                    halt (1);
                 end;
             end
 
@@ -321,7 +321,7 @@ begin
                 else if CompareText (Elem [1], 'CLNEQ') = 0 then Bin [BP] := $f0
                 else begin
                     writeln ('Error (line ', LP, '): no such instruction');
-                    halt;
+                    halt (1);
                 end;
 
                 //Check for incorrect number of arguments
@@ -389,7 +389,7 @@ begin
         end;
         Count := Count + 1;
     end;
-    if AllRefsResolved = false then halt;
+    if AllRefsResolved = false then halt (1);
 
     //Set the end pointer and reset the byte pointer to the start of the program
     EP := BP;
@@ -402,7 +402,7 @@ begin
     {$i+}
     if IOResult <> 0 then begin
         writeln ('Error: program file cannot be written to');
-        halt;
+        halt (1);
     end;
     repeat
         write (Prog, Bin [BP]);