diff --git a/assembler.pas b/assembler.pas
index 179b6e8..f226dd0 100644
--- a/assembler.pas
+++ b/assembler.pas
@@ -9,7 +9,9 @@ type
     LblRec = record
         Addr: word;
         Lbl: ansistring;
+        Line: integer;
         Offset: integer;
+        Resolved: boolean;
     end;
 
 var
@@ -17,6 +19,7 @@ var
     Line, DatOrg: ansistring; //Line of assembly and data or org element
     Elem: array [0 .. 4] of ansistring; //Parsed elements
     Lbl, Ref: array [0 .. $ffff] of LblRec; //Label and reference tables
+    AllRefsResolved: boolean; //Whether there are any references to nonexistent labels
     Addr, BP, SP, EP: word; //Address argument and byte, start, and end pointers
     Bin: array [0 .. $ffef] of byte; //Assembled binary
     Prog: file of byte; //Program file
@@ -136,7 +139,9 @@ begin
             //Store the reference in the table
             Ref [Count] .Addr := BP + A;
             Ref [Count] .Lbl := Elem [I];
+            Ref [Count] .Line := LP;
             Ref [Count] .Offset := Offset;
+            Ref [Count] .Resolved := false;
             //Placeholder
             Addr := 0;
             Offset := 0;
@@ -222,6 +227,7 @@ begin
                                 if BP + Ref [Count] .Offset <= $ffff then begin
                                     Bin [Ref [Count] .Addr] := (BP + Ref [Count] .Offset) shr 8;
                                     Bin [Ref [Count] .Addr + 1] := (BP + Ref [Count] .Offset) and $00ff;
+                                    Ref [Count] .Resolved := true;
                                 end
                                 else RefError;
                             end
@@ -373,6 +379,18 @@ begin
 
     until eof ();
 
+    //Check that all references to labels were properly resolved
+    AllRefsResolved := true;
+    Count := 0;
+    while Ref [Count] .Lbl <> '' do begin
+        if Ref [Count] .Resolved = false then begin
+            writeln ('Error (line ', Ref [Count] .Line, '): label not found: ', Ref [Count] .Lbl);
+            AllRefsResolved := false;
+        end;
+        Count := Count + 1;
+    end;
+    if AllRefsResolved = false then halt;
+
     //Set the end pointer and reset the byte pointer to the start of the program
     EP := BP;
     BP := SP;