diff --git a/asn.h b/asn.h
index 52a184c9..90809ef9 100644
--- a/asn.h
+++ b/asn.h
@@ -13,6 +13,13 @@
 #include "queue.h"
 #include "misc.h"
 
+// Issue 340
+#if CRYPTOPP_GCC_DIAGNOSTIC_AVAILABLE
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Wconversion"
+# pragma GCC diagnostic ignored "-Wsign-conversion"
+#endif
+
 NAMESPACE_BEGIN(CryptoPP)
 
 //! \brief ASN.1 types
@@ -543,4 +550,9 @@ inline ::CryptoPP::OID operator+(const ::CryptoPP::OID &lhs, unsigned long rhs)
 
 NAMESPACE_END
 
+// Issue 340
+#if CRYPTOPP_GCC_DIAGNOSTIC_AVAILABLE
+# pragma GCC diagnostic pop
+#endif
+
 #endif
diff --git a/cpu.h b/cpu.h
index e42792ba..b41a0b62 100644
--- a/cpu.h
+++ b/cpu.h
@@ -9,6 +9,13 @@
 
 #include "config.h"
 
+// Issue 340
+#if CRYPTOPP_GCC_DIAGNOSTIC_AVAILABLE
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Wconversion"
+# pragma GCC diagnostic ignored "-Wsign-conversion"
+#endif
+
 // ARM32/ARM64 Headers
 #if (CRYPTOPP_BOOL_ARM32 || CRYPTOPP_BOOL_ARM64)
 # if defined(__GNUC__)
@@ -602,4 +609,9 @@ inline int GetCacheLineSize()
 
 NAMESPACE_END
 
+// Issue 340
+#if CRYPTOPP_GCC_DIAGNOSTIC_AVAILABLE
+# pragma GCC diagnostic pop
+#endif
+
 #endif  // CRYPTOPP_CPU_H
diff --git a/cryptlib.cpp b/cryptlib.cpp
index d58c71d5..3bd064ed 100644
--- a/cryptlib.cpp
+++ b/cryptlib.cpp
@@ -131,13 +131,13 @@ void SimpleKeyingInterface::ThrowIfInvalidIV(const byte *iv)
 size_t SimpleKeyingInterface::ThrowIfInvalidIVLength(int size)
 {
 	if (size < 0)
-		return IVSize();
+		return (size_t)IVSize();
 	else if ((size_t)size < MinIVLength())
 		throw InvalidArgument(GetAlgorithm().AlgorithmName() + ": IV length " + IntToString(size) + " is less than the minimum of " + IntToString(MinIVLength()));
 	else if ((size_t)size > MaxIVLength())
 		throw InvalidArgument(GetAlgorithm().AlgorithmName() + ": IV length " + IntToString(size) + " exceeds the maximum of " + IntToString(MaxIVLength()));
 	else
-		return size;
+		return (size_t)size;
 }
 
 const byte * SimpleKeyingInterface::GetIVAndThrowIfInvalid(const NameValuePairs &params, size_t &size)
@@ -298,7 +298,7 @@ byte RandomNumberGenerator::GenerateByte()
 word32 RandomNumberGenerator::GenerateWord32(word32 min, word32 max)
 {
 	const word32 range = max-min;
-	const int maxBits = BitPrecision(range);
+	const unsigned int maxBits = BitPrecision(range);
 
 	word32 value;
 
@@ -721,6 +721,13 @@ size_t BufferedTransformation::PutWord32(word32 value, ByteOrder order, bool blo
 	return ChannelPutWord32(DEFAULT_CHANNEL, value, order, blocking);
 }
 
+// Issue 340
+#if CRYPTOPP_GCC_DIAGNOSTIC_AVAILABLE
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Wconversion"
+# pragma GCC diagnostic ignored "-Wsign-conversion"
+#endif
+
 size_t BufferedTransformation::PeekWord16(word16 &value, ByteOrder order) const
 {
 	byte buf[2] = {0, 0};
@@ -747,6 +754,11 @@ size_t BufferedTransformation::PeekWord32(word32 &value, ByteOrder order) const
 	return len;
 }
 
+// Issue 340
+#if CRYPTOPP_GCC_DIAGNOSTIC_AVAILABLE
+# pragma GCC diagnostic pop
+#endif
+
 size_t BufferedTransformation::GetWord16(word16 &value, ByteOrder order)
 {
 	return (size_t)Skip(PeekWord16(value, order));
diff --git a/gf2n.cpp b/gf2n.cpp
index 99380e13..2bc5331a 100644
--- a/gf2n.cpp
+++ b/gf2n.cpp
@@ -18,6 +18,12 @@
 
 #include <iostream>
 
+// Issue 340
+#if CRYPTOPP_GCC_DIAGNOSTIC_AVAILABLE
+# pragma GCC diagnostic ignored "-Wconversion"
+# pragma GCC diagnostic ignored "-Wsign-conversion"
+#endif
+
 NAMESPACE_BEGIN(CryptoPP)
 
 PolynomialMod2::PolynomialMod2()
diff --git a/integer.cpp b/integer.cpp
index b24b7795..4dc9dfcb 100644
--- a/integer.cpp
+++ b/integer.cpp
@@ -13,6 +13,12 @@
 # pragma GCC diagnostic ignored "-Wunused-but-set-variable"
 #endif
 
+// Issue 340
+#if CRYPTOPP_GCC_DIAGNOSTIC_AVAILABLE
+# pragma GCC diagnostic ignored "-Wconversion"
+# pragma GCC diagnostic ignored "-Wsign-conversion"
+#endif
+
 #ifndef CRYPTOPP_IMPORTS
 
 #include "integer.h"
diff --git a/misc.h b/misc.h
index ccbb5db9..2793d06e 100644
--- a/misc.h
+++ b/misc.h
@@ -19,6 +19,13 @@
 # endif
 #endif
 
+// Issue 340
+#if CRYPTOPP_GCC_DIAGNOSTIC_AVAILABLE
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Wconversion"
+# pragma GCC diagnostic ignored "-Wsign-conversion"
+#endif
+
 #include "cryptlib.h"
 #include "stdcpp.h"
 #include "smartptr.h"
@@ -2428,4 +2435,8 @@ NAMESPACE_END
 # pragma warning(pop)
 #endif
 
+#if CRYPTOPP_GCC_DIAGNOSTIC_AVAILABLE
+# pragma GCC diagnostic pop
+#endif
+
 #endif
diff --git a/modes.h b/modes.h
index d015259f..2a22024c 100644
--- a/modes.h
+++ b/modes.h
@@ -13,6 +13,13 @@
 #include "argnames.h"
 #include "algparam.h"
 
+// Issue 340
+#if CRYPTOPP_GCC_DIAGNOSTIC_AVAILABLE
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Wconversion"
+# pragma GCC diagnostic ignored "-Wsign-conversion"
+#endif
+
 NAMESPACE_BEGIN(CryptoPP)
 
 //! \class CipherModeDocumentation
@@ -482,4 +489,9 @@ typedef CTR_Mode_ExternalCipher::Encryption CounterMode;
 
 NAMESPACE_END
 
+// Issue 340
+#if CRYPTOPP_GCC_DIAGNOSTIC_AVAILABLE
+# pragma GCC diagnostic pop
+#endif
+
 #endif
diff --git a/seckey.h b/seckey.h
index b512a3a2..92e38395 100644
--- a/seckey.h
+++ b/seckey.h
@@ -1,21 +1,27 @@
 // seckey.h - written and placed in the public domain by Wei Dai
 
-//! \file
+//! \file seckey.h
 //! \brief Classes and functions for implementing secret key algorithms.
 
 #ifndef CRYPTOPP_SECKEY_H
 #define CRYPTOPP_SECKEY_H
 
 #include "config.h"
+#include "cryptlib.h"
+#include "misc.h"
+#include "simple.h"
 
 #if CRYPTOPP_MSC_VERSION
 # pragma warning(push)
 # pragma warning(disable: 4189)
 #endif
 
-#include "cryptlib.h"
-#include "misc.h"
-#include "simple.h"
+// Issue 340
+#if CRYPTOPP_GCC_DIAGNOSTIC_AVAILABLE
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Wconversion"
+# pragma GCC diagnostic ignored "-Wsign-conversion"
+#endif
 
 NAMESPACE_BEGIN(CryptoPP)
 
@@ -442,4 +448,9 @@ NAMESPACE_END
 # pragma warning(pop)
 #endif
 
+// Issue 340
+#if CRYPTOPP_GCC_DIAGNOSTIC_AVAILABLE
+# pragma GCC diagnostic pop
+#endif
+
 #endif