diff --git a/libc/include/stdio.h b/libc/include/stdio.h
index fddad2f2e..31e926176 100644
--- a/libc/include/stdio.h
+++ b/libc/include/stdio.h
@@ -466,8 +466,7 @@ __attribute__((__format__ (printf, 3, 0)))
 __attribute__((__nonnull__ (3)))
 int vsnprintf(char *dest, size_t size, const char *format, __va_list ap)
 {
-    return __builtin___vsnprintf_chk(dest, size, 0,
-        __builtin_object_size(dest, 0), format, ap);
+    return __builtin___vsnprintf_chk(dest, size, 0, __bos(dest), format, ap);
 }
 
 __BIONIC_FORTIFY_INLINE
@@ -475,8 +474,7 @@ __attribute__((__format__ (printf, 2, 0)))
 __attribute__((__nonnull__ (2)))
 int vsprintf(char *dest, const char *format, __va_list ap)
 {
-    return __builtin___vsprintf_chk(dest, 0,
-        __builtin_object_size(dest, 0), format, ap);
+    return __builtin___vsprintf_chk(dest, 0, __bos(dest), format, ap);
 }
 
 __BIONIC_FORTIFY_INLINE
@@ -485,7 +483,7 @@ __attribute__((__nonnull__ (3)))
 int snprintf(char *str, size_t size, const char *format, ...)
 {
     return __builtin___snprintf_chk(str, size, 0,
-        __builtin_object_size(str, 0), format, __builtin_va_arg_pack());
+        __bos(str), format, __builtin_va_arg_pack());
 }
 
 __BIONIC_FORTIFY_INLINE
@@ -508,7 +506,7 @@ extern char *__fgets_chk(char *, int, FILE *, size_t);
 __BIONIC_FORTIFY_INLINE
 char *fgets(char *dest, int size, FILE *stream)
 {
-    size_t bos = __builtin_object_size(dest, 0);
+    size_t bos = __bos(dest);
 
     // Compiler can prove, at compile time, that the passed in size
     // is always negative. Force a compiler error.
diff --git a/libc/include/string.h b/libc/include/string.h
index 02d815143..c0df686e3 100644
--- a/libc/include/string.h
+++ b/libc/include/string.h
@@ -116,7 +116,7 @@ void *memmove (void *dest, const void *src, size_t len) {
 
 __BIONIC_FORTIFY_INLINE
 char *strcpy(char *dest, const char *src) {
-    return __builtin___strcpy_chk(dest, src, __builtin_object_size (dest, 0));
+    return __builtin___strcpy_chk(dest, src, __bos(dest));
 }
 
 extern void __strncpy_error()
@@ -133,12 +133,12 @@ char *strncpy(char *dest, const char *src, size_t n) {
 
 __BIONIC_FORTIFY_INLINE
 char *strcat(char *dest, const char *src) {
-    return __builtin___strcat_chk(dest, src, __builtin_object_size (dest, 0));
+    return __builtin___strcat_chk(dest, src, __bos(dest));
 }
 
 __BIONIC_FORTIFY_INLINE
 char *strncat(char *dest, const char *src, size_t n) {
-    return __builtin___strncat_chk(dest, src, n, __builtin_object_size (dest, 0));
+    return __builtin___strncat_chk(dest, src, n, __bos(dest));
 }
 
 __BIONIC_FORTIFY_INLINE
@@ -154,7 +154,7 @@ extern size_t __strlcpy_chk(char *, const char *, size_t, size_t);
 
 __BIONIC_FORTIFY_INLINE
 size_t strlcpy(char *dest, const char *src, size_t size) {
-    size_t bos = __builtin_object_size(dest, 0);
+    size_t bos = __bos(dest);
 
     // Compiler doesn't know destination size. Don't call __strlcpy_chk
     if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
@@ -185,7 +185,7 @@ extern size_t __strlcat_chk(char *, const char *, size_t, size_t);
 
 __BIONIC_FORTIFY_INLINE
 size_t strlcat(char *dest, const char *src, size_t size) {
-    size_t bos = __builtin_object_size(dest, 0);
+    size_t bos = __bos(dest);
 
     // Compiler doesn't know destination size. Don't call __strlcat_chk
     if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
@@ -211,7 +211,7 @@ extern size_t __strlen_chk(const char *, size_t);
 
 __BIONIC_FORTIFY_INLINE
 size_t strlen(const char *s) {
-    size_t bos = __builtin_object_size(s, 0);
+    size_t bos = __bos(s);
 
     // Compiler doesn't know destination size. Don't call __strlen_chk
     if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
@@ -230,7 +230,7 @@ extern char* __strchr_chk(const char *, int, size_t);
 
 __BIONIC_FORTIFY_INLINE
 char* strchr(const char *s, int c) {
-    size_t bos = __builtin_object_size(s, 0);
+    size_t bos = __bos(s);
 
     // Compiler doesn't know destination size. Don't call __strchr_chk
     if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {