diff --git a/README.md b/README.md
index b1e8c85f..60c346f0 100644
--- a/README.md
+++ b/README.md
@@ -24,6 +24,7 @@ Recent significant changes to the library
 
 XXX 2018:
 
+* Problem with BLAKE2s and BLAKE2b HMAC mode when the data was zero-length.
 * KeyRing for storing key pairs and other key material in EEPROM or Flash.
 * Add better functions to Curve25519 and Ed25519 for generating key pairs.
 * Noise and NoiseLink protocols.
diff --git a/libraries/Crypto/BLAKE2b.cpp b/libraries/Crypto/BLAKE2b.cpp
index 7352ec06..d19f7353 100644
--- a/libraries/Crypto/BLAKE2b.cpp
+++ b/libraries/Crypto/BLAKE2b.cpp
@@ -240,7 +240,7 @@ void BLAKE2b::resetHMAC(const void *key, size_t keyLen)
 {
     formatHMACKey(state.m, key, keyLen, 0x36);
     state.lengthLow += 128;
-    processChunk(0);
+    state.chunkSize = 128;
 }
 
 void BLAKE2b::finalizeHMAC(const void *key, size_t keyLen, void *hash, size_t hashLen)
@@ -249,7 +249,7 @@ void BLAKE2b::finalizeHMAC(const void *key, size_t keyLen, void *hash, size_t ha
     finalize(temp, sizeof(temp));
     formatHMACKey(state.m, key, keyLen, 0x5C);
     state.lengthLow += 128;
-    processChunk(0);
+    state.chunkSize = 128;
     update(temp, sizeof(temp));
     finalize(hash, hashLen);
     clean(temp);
diff --git a/libraries/Crypto/BLAKE2s.cpp b/libraries/Crypto/BLAKE2s.cpp
index a707ff7e..2a548538 100644
--- a/libraries/Crypto/BLAKE2s.cpp
+++ b/libraries/Crypto/BLAKE2s.cpp
@@ -234,7 +234,7 @@ void BLAKE2s::resetHMAC(const void *key, size_t keyLen)
 {
     formatHMACKey(state.m, key, keyLen, 0x36);
     state.length += 64;
-    processChunk(0);
+    state.chunkSize = 64;
 }
 
 void BLAKE2s::finalizeHMAC(const void *key, size_t keyLen, void *hash, size_t hashLen)
@@ -243,7 +243,7 @@ void BLAKE2s::finalizeHMAC(const void *key, size_t keyLen, void *hash, size_t ha
     finalize(temp, sizeof(temp));
     formatHMACKey(state.m, key, keyLen, 0x5C);
     state.length += 64;
-    processChunk(0);
+    state.chunkSize = 64;
     update(temp, sizeof(temp));
     finalize(hash, hashLen);
     clean(temp);