diff --git a/include/ctype.h b/include/ctype.h
index b76ea42ca1e..75e7a77dbfb 100644
--- a/include/ctype.h
+++ b/include/ctype.h
@@ -143,7 +143,7 @@ int isgraph(int c);
 #ifdef __cplusplus
 static inline int iscntrl(int c)
 {
-  return !isprint(c);
+  return c < 0x20 || c == 0x7F;
 }
 #else
 int iscntrl(int c);
diff --git a/libs/libc/ctype/lib_iscntrl.c b/libs/libc/ctype/lib_iscntrl.c
index 410377b193e..7f8c44ae06b 100644
--- a/libs/libc/ctype/lib_iscntrl.c
+++ b/libs/libc/ctype/lib_iscntrl.c
@@ -30,5 +30,5 @@
 
 int iscntrl(int c)
 {
-  return !isprint(c);
+  return c < 0x20 || c == 0x7F;
 }