diff --git a/src/common/crypto.h b/src/common/crypto.h
index c15fe730..bb7d361b 100644
--- a/src/common/crypto.h
+++ b/src/common/crypto.h
@@ -37,6 +37,9 @@ class AES_GCM_CipherContext : public SymmetricCryptContextBase
 
 	// Initialize context with the specified private key, IV size, and tag size
 	bool InitCipher( const void *pKey, size_t cbKey, size_t cbIV, size_t cbTag, bool bEncrypt );
+
+	// Determine whether AES_GCM is supported on this system + crypto backend
+	static bool IsAvailable();
 };
 
 class AES_GCM_EncryptContext : public AES_GCM_CipherContext
diff --git a/src/common/crypto_bcrypt.cpp b/src/common/crypto_bcrypt.cpp
index 4b94430e..d9cba30b 100644
--- a/src/common/crypto_bcrypt.cpp
+++ b/src/common/crypto_bcrypt.cpp
@@ -33,6 +33,7 @@ typedef struct _BCryptContext {
 	ULONG cbKeyObject;
 
 	_BCryptContext() {
+		hAlgAES = INVALID_HANDLE_VALUE;
 		hKey = INVALID_HANDLE_VALUE;
 		pbKeyObject = NULL;
 		cbKeyObject = 0;
@@ -121,6 +122,15 @@ bool AES_GCM_CipherContext::InitCipher( const void *pKey, size_t cbKey, size_t c
 	return true;
 }
 
+bool AES_GCM_CipherContext::IsAvailable()
+{
+	BCryptContext ctx;
+	if ( BCryptOpenAlgorithmProvider( &ctx.hAlgAES, BCRYPT_AES_ALGORITHM, nullptr, 0 ) != 0 )
+		return false;
+	AssertFatal( ctx.hAlgAES != INVALID_HANDLE_VALUE );
+	return true;
+}
+
 bool AES_GCM_EncryptContext::Encrypt(
 		const void *pPlaintextData, size_t cbPlaintextData,
 		const void *pIV,
diff --git a/src/common/crypto_libsodium.cpp b/src/common/crypto_libsodium.cpp
index d78bd089..3c45c7b9 100644
--- a/src/common/crypto_libsodium.cpp
+++ b/src/common/crypto_libsodium.cpp
@@ -44,6 +44,16 @@ bool AES_GCM_CipherContext::InitCipher( const void *pKey, size_t cbKey, size_t c
 	return true;
 }
 
+bool AES_GCM_CipherContext::IsAvailable()
+{
+	// Libsodium requires AES and CLMUL instructions for AES-GCM, available in
+	// Intel "Westmere" and up. 90.41% of Steam users have this as of the
+	// November 2019 survey.
+	// Libsodium recommends ChaCha20-Poly1305 in software if you've not got AES support
+	// in hardware.
+	return crypto_aead_aes256gcm_is_available() == 1;
+}
+
 bool AES_GCM_EncryptContext::Encrypt(
 		const void *pPlaintextData, size_t cbPlaintextData,
 		const void *pIV,
diff --git a/src/common/crypto_openssl.cpp b/src/common/crypto_openssl.cpp
index e31e2a95..6f94a910 100644
--- a/src/common/crypto_openssl.cpp
+++ b/src/common/crypto_openssl.cpp
@@ -149,6 +149,11 @@ bool AES_GCM_CipherContext::InitCipher( const void *pKey, size_t cbKey, size_t c
 	return true;
 }
 
+bool AES_GCM_CipherContext::IsAvailable()
+{
+	return true;
+}
+
 bool AES_GCM_EncryptContext::Encrypt(
 		const void *pPlaintextData, size_t cbPlaintextData,
 		const void *pIV,
diff --git a/src/steamnetworkingsockets/clientlib/steamnetworkingsockets_connections.cpp b/src/steamnetworkingsockets/clientlib/steamnetworkingsockets_connections.cpp
index fd823c2f..cc402752 100644
--- a/src/steamnetworkingsockets/clientlib/steamnetworkingsockets_connections.cpp
+++ b/src/steamnetworkingsockets/clientlib/steamnetworkingsockets_connections.cpp
@@ -1037,14 +1037,17 @@ void CSteamNetworkConnectionBase::ClearCrypto()
 void CSteamNetworkConnectionBase::ClearLocalCrypto()
 {
 	AssertLocksHeldByCurrentThread();
-	m_eNegotiatedCipher = k_ESteamNetworkingSocketsCipher_INVALID;
-	m_cbEncryptionOverhead = k_cbAESGCMTagSize;
 	m_keyExchangePrivateKeyLocal.Wipe();
 	m_msgCryptLocal.Clear();
 	m_msgSignedCryptLocal.Clear();
 	m_bCryptKeysValid = false;
-	m_cryptContextSend.Wipe();
-	m_cryptContextRecv.Wipe();
+	if (m_eNegotiatedCipher != k_ESteamNetworkingSocketsCipher_NULL)
+	{
+		m_cryptContextSend.Wipe();
+		m_cryptContextRecv.Wipe();
+	}
+	m_eNegotiatedCipher = k_ESteamNetworkingSocketsCipher_INVALID;
+	m_cbEncryptionOverhead = k_cbAESGCMTagSize;
 	m_cryptIVSend.Wipe();
 	m_cryptIVRecv.Wipe();
 }
@@ -1219,19 +1222,29 @@ void CSteamNetworkConnectionBase::SetCryptoCipherList()
 			// V
 		case 0:
 			// Not allowed
-			m_msgCryptLocal.add_ciphers( k_ESteamNetworkingSocketsCipher_AES_256_GCM );
+			if (AES_GCM_CipherContext::IsAvailable())
+			{
+				m_msgCryptLocal.add_ciphers( k_ESteamNetworkingSocketsCipher_AES_256_GCM );
+			}
+			Assert( m_msgCryptLocal.ciphers_size() > 0 );
 			break;
 
 		case 1:
 			// Allowed, but prefer encrypted
-			m_msgCryptLocal.add_ciphers( k_ESteamNetworkingSocketsCipher_AES_256_GCM );
+			if (AES_GCM_CipherContext::IsAvailable())
+			{
+				m_msgCryptLocal.add_ciphers( k_ESteamNetworkingSocketsCipher_AES_256_GCM );
+			}
 			m_msgCryptLocal.add_ciphers( k_ESteamNetworkingSocketsCipher_NULL );
 			break;
 
 		case 2:
 			// Allowed, preferred
 			m_msgCryptLocal.add_ciphers( k_ESteamNetworkingSocketsCipher_NULL );
-			m_msgCryptLocal.add_ciphers( k_ESteamNetworkingSocketsCipher_AES_256_GCM );
+			if (AES_GCM_CipherContext::IsAvailable())
+			{
+				m_msgCryptLocal.add_ciphers( k_ESteamNetworkingSocketsCipher_AES_256_GCM );
+			}
 			break;
 
 		case 3:
@@ -1693,13 +1706,16 @@ bool CSteamNetworkConnectionBase::BFinishCryptoHandshake( bool bServer )
 		V_memcpy( pStart, &expandTemp, sizeof(SHA256Digest_t) );
 	}
 
-	// Set encryption keys into the contexts, and set parameters
-	if (
-		!m_cryptContextSend.Init( cryptKeySend.m_buf, cryptKeySend.k_nSize, m_cryptIVSend.k_nSize, k_cbAESGCMTagSize )
-		|| !m_cryptContextRecv.Init( cryptKeyRecv.m_buf, cryptKeyRecv.k_nSize, m_cryptIVRecv.k_nSize, k_cbAESGCMTagSize ) )
+	if (m_eNegotiatedCipher != k_ESteamNetworkingSocketsCipher_NULL)
 	{
-		ConnectionState_ProblemDetectedLocally( k_ESteamNetConnectionEnd_Remote_BadCrypt, "Error initializing crypto" );
-		return false;
+		// Set encryption keys into the contexts, and set parameters
+		if (
+			!m_cryptContextSend.Init( cryptKeySend.m_buf, cryptKeySend.k_nSize, m_cryptIVSend.k_nSize, k_cbAESGCMTagSize )
+			|| !m_cryptContextRecv.Init( cryptKeyRecv.m_buf, cryptKeyRecv.k_nSize, m_cryptIVRecv.k_nSize, k_cbAESGCMTagSize ) )
+		{
+			ConnectionState_ProblemDetectedLocally( k_ESteamNetConnectionEnd_Remote_BadCrypt, "Error initializing crypto" );
+			return false;
+		}
 	}
 
 	//