diff --git a/spec/builtin_contracts_spec.rb b/spec/builtin_contracts_spec.rb
index <HASH>..<HASH> 100644
--- a/spec/builtin_contracts_spec.rb
+++ b/spec/builtin_contracts_spec.rb
@@ -22,6 +22,10 @@ RSpec.describe "Contracts:" do
       expect { @o.pos_test(1) }.to_not raise_error
     end
 
+    it "should fail for 0" do
+      expect { @o.pos_test(0) }.to raise_error(ContractError)
+    end
+
     it "should fail for negative numbers" do
       expect { @o.pos_test(-1) }.to raise_error(ContractError)
     end
@@ -32,6 +36,10 @@ RSpec.describe "Contracts:" do
       expect { @o.neg_test(-1) }.to_not raise_error
     end
 
+    it "should fail for 0" do
+      expect { @o.neg_test(0) }.to raise_error(ContractError)
+    end
+
     it "should fail for positive numbers" do
       expect { @o.neg_test(1) }.to raise_error(ContractError)
     end
Add tests for 0 against Pos and Neg.