diff --git a/library/pk_wrap.c b/library/pk_wrap.c
index 78cee74..e567e63 100644
--- a/library/pk_wrap.c
+++ b/library/pk_wrap.c
@@ -475,6 +475,11 @@
 #endif /* MBEDTLS_ECP_C */
 
 #if defined(MBEDTLS_USE_TINYCRYPT)
+
+/*
+ * An ASN.1 encoded signature is a sequence of two ASN.1 integers. Parse one of
+ * those integers and convert it to the fixed-length encoding.
+ */
 static int extract_ecdsa_sig_int( unsigned char **from, const unsigned char *end,
                                   unsigned char *to, size_t to_len )
 {