1 files changed, 2 insertions, 0 deletions

diff --git a/asm.rb b/asm.rb
index 4883edb..686f9c1 100755
--- a/asm.rb
+++ b/asm.rb
@@ -57,7 +57,9 @@ $code.each_with_index() do | line, i |
       op |= $labels[$1]
     elsif $labels.key?(ref)
       target = $labels[ref] - (i + 1)
+      throw "Jump too far forward" if target > 0x7f
       target += 0x80 if target < 0
+      throw "Jump too far backward" if target < 0
       op |= target
     else
       throw "I don't understand #{ref.inspect()}"