diff --git a/cryptography/hazmat/primitives/constant_time.py b/cryptography/hazmat/primitives/constant_time.py
index a835150..6502803 100644
--- a/cryptography/hazmat/primitives/constant_time.py
+++ b/cryptography/hazmat/primitives/constant_time.py
@@ -20,17 +20,16 @@
 
 _ffi = cffi.FFI()
 _ffi.cdef("""
-bool Cryptography_constant_time_bytes_eq(uint8_t *, size_t, uint8_t *, size_t);
+uint8_t Cryptography_constant_time_bytes_eq(uint8_t *, size_t, uint8_t *,
+                                            size_t);
 """)
 _lib = _ffi.verify("""
-#include <stdbool.h>
-
-bool Cryptography_constant_time_bytes_eq(uint8_t *a, size_t len_a, uint8_t *b,
-                                         size_t len_b) {
+uint8_t Cryptography_constant_time_bytes_eq(uint8_t *a, size_t len_a,
+                                            uint8_t *b, size_t len_b) {
     size_t i = 0;
     uint8_t mismatch = 0;
     if (len_a != len_b) {
-        return false;
+        return 0;
     }
     for (i = 0; i < len_a; i++) {
         mismatch |= a[i] ^ b[i];
diff --git a/cryptography/hazmat/primitives/padding.py b/cryptography/hazmat/primitives/padding.py
index cfa90db..9729827 100644
--- a/cryptography/hazmat/primitives/padding.py
+++ b/cryptography/hazmat/primitives/padding.py
@@ -21,11 +21,9 @@
 
 _ffi = cffi.FFI()
 _ffi.cdef("""
-bool Cryptography_check_pkcs7_padding(const uint8_t *, uint8_t);
+uint8_t Cryptography_check_pkcs7_padding(const uint8_t *, uint8_t);
 """)
 _lib = _ffi.verify("""
-#include <stdbool.h>
-
 /* Returns the value of the input with the most-significant-bit copied to all
    of the bits. */
 static uint8_t Cryptography_DUPLICATE_MSB_TO_ALL(uint8_t a) {
@@ -39,7 +37,7 @@
     return Cryptography_DUPLICATE_MSB_TO_ALL(a);
 }
 
-bool Cryptography_check_pkcs7_padding(const uint8_t *data, uint8_t block_len) {
+uint8_t Cryptography_check_pkcs7_padding(const uint8_t *data, uint8_t block_len) {
     uint8_t i;
     uint8_t pad_size = data[block_len - 1];
     uint8_t mismatch = 0;