diff --git a/libguile/vm-i-system.c b/libguile/vm-i-system.c
index d55d6e2..427a2fc 100644
--- a/libguile/vm-i-system.c
+++ b/libguile/vm-i-system.c
@@ -406,12 +406,12 @@ VM_DEFINE_INSTRUCTION (31, br, "br", 2, 0, 0)
 
 VM_DEFINE_INSTRUCTION (32, br_if, "br-if", 2, 0, 0)
 {
-  BR (!SCM_FALSEP (*sp));
+  BR (scm_is_true_and_not_lisp_nil (*sp));
 }
 
 VM_DEFINE_INSTRUCTION (33, br_if_not, "br-if-not", 2, 0, 0)
 {
-  BR (SCM_FALSEP (*sp));
+  BR (scm_is_false_or_lisp_nil (*sp));
 }
 
 VM_DEFINE_INSTRUCTION (34, br_if_eq, "br-if-eq", 2, 0, 0)
@@ -428,12 +428,12 @@ VM_DEFINE_INSTRUCTION (35, br_if_not_eq, "br-if-not-eq", 2, 0, 0)
 
 VM_DEFINE_INSTRUCTION (36, br_if_null, "br-if-null", 2, 0, 0)
 {
-  BR (SCM_NULLP (*sp));
+  BR (scm_is_null_or_lisp_nil (*sp));
 }
 
 VM_DEFINE_INSTRUCTION (37, br_if_not_null, "br-if-not-null", 2, 0, 0)
 {
-  BR (!SCM_NULLP (*sp));
+  BR (!scm_is_null_or_lisp_nil (*sp));
 }
 
 
diff --git a/libguile/vm-i-scheme.c b/libguile/vm-i-scheme.c
index 5de39a2..40781ff 100644
--- a/libguile/vm-i-scheme.c
+++ b/libguile/vm-i-scheme.c
@@ -32,13 +32,13 @@
 VM_DEFINE_FUNCTION (80, not, "not", 1)
 {
   ARGS1 (x);
-  RETURN (SCM_BOOL (SCM_FALSEP (x)));
+  RETURN (SCM_BOOL (scm_is_false_or_lisp_nil (x)));
 }
 
 VM_DEFINE_FUNCTION (81, not_not, "not-not", 1)
 {
   ARGS1 (x);
-  RETURN (SCM_BOOL (!SCM_FALSEP (x)));
+  RETURN (SCM_BOOL (!scm_is_false_or_lisp_nil (x)));
 }
 
 VM_DEFINE_FUNCTION (82, eq, "eq?", 2)
@@ -56,13 +56,13 @@ VM_DEFINE_FUNCTION (83, not_eq, "not-eq?", 2)
 VM_DEFINE_FUNCTION (84, nullp, "null?", 1)
 {
   ARGS1 (x);
-  RETURN (SCM_BOOL (SCM_NULLP (x)));
+  RETURN (SCM_BOOL (scm_is_null_or_lisp_nil (x)));
 }
 
 VM_DEFINE_FUNCTION (85, not_nullp, "not-null?", 1)
 {
   ARGS1 (x);
-  RETURN (SCM_BOOL (!SCM_NULLP (x)));
+  RETURN (SCM_BOOL (!scm_is_null_or_lisp_nil (x)));
 }
 
 VM_DEFINE_FUNCTION (86, eqv, "eqv?", 2)