diff --git a/cryptography/hazmat/bindings/commoncrypto/seckey.py b/cryptography/hazmat/bindings/commoncrypto/seckey.py
index 38aaece..5e4b6da 100644
--- a/cryptography/hazmat/bindings/commoncrypto/seckey.py
+++ b/cryptography/hazmat/bindings/commoncrypto/seckey.py
@@ -23,6 +23,7 @@
 
 FUNCTIONS = """
 OSStatus SecKeyGeneratePair(CFDictionaryRef, SecKeyRef *, SecKeyRef *);
+size_t SecKeyGetBlockSize(SecKeyRef);
 """
 
 MACROS = """