diff --git a/stdlib/stdlib.lsp b/stdlib/stdlib.lsp
index 34b9f6e..6fd241e 100644
--- a/stdlib/stdlib.lsp
+++ b/stdlib/stdlib.lsp
@@ -1,5 +1,5 @@
 ; not a bool
-(defun not (x) (if x 0 1))
+(defun not (x) (if x nil 1))
 
 (defun is-pos? (n) (> n 0))
 (defun is-neg? (n) (< n 0))
diff --git a/tests/test.lsp b/tests/test.lsp
index 5714065..394a881 100644
--- a/tests/test.lsp
+++ b/tests/test.lsp
@@ -24,6 +24,9 @@
 (ut::define-test "result of (and (> 1 1) (> 1 2))" '(ut::assert-false (and (> 1 1) (> 1 2))))
 (ut::define-test "result of (or (> 1 1) (> 2 1))" '(ut::assert-true (or (> 1 1) (> 2 1))))
 
+(ut::define-test "result of (not 1)" '(ut::assert-false (not 1)))
+(ut::define-test "result of (not nil)" '(ut::assert-true (not nil)))
+
 
 (ut::define-test "result of (member '(1 2 3) 1" '(ut::assert-true (member '(1 2 3) 1)))
 (ut::define-test "result of (member '(1 2 3) 3" '(ut::assert-true (member '(1 2 3) 3)))