diff --git a/src/crypto.c b/src/crypto.c
index 1c2d2db2..7e7085f6 100644
--- a/src/crypto.c
+++ b/src/crypto.c
@@ -836,7 +836,7 @@ bool crypto_derive_pairwise_ptk(const uint8_t *pmk, size_t pmk_len,
 }
 
 /* Defined in 802.11-2012, Section 11.6.1.7.3 PMK-R0 */
-bool crypto_derive_pmk_r0(const uint8_t *xxkey,
+bool crypto_derive_pmk_r0(const uint8_t *xxkey, size_t xxkey_len,
 				const uint8_t *ssid, size_t ssid_len,
 				uint16_t mdid,
 				const uint8_t *r0khid, size_t r0kh_len,
@@ -869,7 +869,7 @@ bool crypto_derive_pmk_r0(const uint8_t *xxkey,
 	memcpy(context + pos, s0khid, ETH_ALEN);
 	pos += ETH_ALEN;
 
-	if (!kdf_sha256(xxkey, 32, "FT-R0", 5, context, pos, output, 48))
+	if (!kdf_sha256(xxkey, xxkey_len, "FT-R0", 5, context, pos, output, 48))
 		goto exit;
 
 	sha256 = l_checksum_new(L_CHECKSUM_SHA256);
diff --git a/src/crypto.h b/src/crypto.h
index 0b7f0275..87676d96 100644
--- a/src/crypto.h
+++ b/src/crypto.h
@@ -116,7 +116,7 @@ bool crypto_derive_pairwise_ptk(const uint8_t *pmk, size_t pmk_len,
 				uint8_t *out_ptk, size_t ptk_len,
 				enum l_checksum_type type);
 
-bool crypto_derive_pmk_r0(const uint8_t *xxkey,
+bool crypto_derive_pmk_r0(const uint8_t *xxkey, size_t xxkey_len,
 				const uint8_t *ssid, size_t ssid_len,
 				uint16_t mdid,
 				const uint8_t *r0khid, size_t r0kh_len,
diff --git a/src/handshake.c b/src/handshake.c
index 19adbfd9..e51e2f92 100644
--- a/src/handshake.c
+++ b/src/handshake.c
@@ -424,7 +424,7 @@ bool handshake_state_derive_ptk(struct handshake_state *s)
 		ie_parse_mobility_domain_from_data(s->mde, s->mde[1] + 2,
 							&mdid, NULL, NULL);
 
-		if (!crypto_derive_pmk_r0(xxkey, s->ssid, s->ssid_len, mdid,
+		if (!crypto_derive_pmk_r0(xxkey, 32, s->ssid, s->ssid_len, mdid,
 						s->r0khid, s->r0khid_len,
 						s->spa,
 						s->pmk_r0, s->pmk_r0_name))