diff --git a/CMakeLists.txt b/CMakeLists.txt
index 773c1210..2b1ec771 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -447,31 +447,61 @@ ELSE(BIGENDIAN EQUAL 0)
 	SET(VMIME_BYTE_ORDER_LITTLE_ENDIAN  0)
 ENDIF(BIGENDIAN EQUAL 0)
 
-SET(VMIME_DEFAULT_8BIT_TYPE  "char")
-SET(VMIME_DEFAULT_16BIT_TYPE "short")
-SET(VMIME_DEFAULT_32BIT_TYPE "int")
 
+CHECK_TYPE_SIZE("char"      SIZEOF_CHAR)
+CHECK_TYPE_SIZE("short"     SIZEOF_SHORT)
+CHECK_TYPE_SIZE("int"       SIZEOF_INT)
+CHECK_TYPE_SIZE("long"      SIZEOF_LONG)
+CHECK_TYPE_SIZE("long long" SIZEOF_LONG_LONG)
+CHECK_TYPE_SIZE("__int64"   SIZEOF___INT64)
 
-SET(
-	VMIME_8BIT_TYPE
-	${VMIME_DEFAULT_8BIT_TYPE}
-	CACHE STRING
-	"The C-language 8-bit type for your platform"
-)
+IF(SIZEOF_CHAR EQUAL 1)
+	SET(VMIME_8BIT_TYPE "char")
+ELSE()
+	MESSAGE(FATAL_ERROR "Cannot determine 8-bit type")
+ENDIF()
 
-SET(
-	VMIME_16BIT_TYPE
-	${VMIME_DEFAULT_16BIT_TYPE}
-	CACHE STRING
-	"The C-language 16-bit type for your platform"
-)
+IF(SIZEOF_INT EQUAL 2)
+	SET(VMIME_16BIT_TYPE "int")
+ELSE()
+	IF(SIZEOF_SHORT EQUAL 2)
+		SET(VMIME_16BIT_TYPE "short")
+	ELSE()
+		MESSAGE(FATAL_ERROR "Cannot determine 16-bit type")
+	ENDIF()
+ENDIF()
 
-SET(
-	VMIME_32BIT_TYPE
-	${VMIME_DEFAULT_32BIT_TYPE}
-	CACHE STRING
-	"The C-language 32-bit type for your platform"
-)
+IF(SIZEOF_INT EQUAL 4)
+	SET(VMIME_32BIT_TYPE "int")
+ELSE()
+	IF(SIZEOF_LONG EQUAL 4)
+		SET(VMIME_32BIT_TYPE "long")
+	ELSE()
+		IF(SIZEOF_LONG_LONG EQUAL 4)
+			SET(VMIME_32BIT_TYPE "long long")
+		ELSE()
+			MESSAGE(FATAL_ERROR "Cannot determine 32-bit type")
+		ENDIF()
+	ENDIF()
+ENDIF()
+
+IF(SIZEOF_INT EQUAL 8)
+	SET(VMIME_64BIT_TYPE "int")
+ELSE()
+	IF(SIZEOF_LONG EQUAL 8)
+		SET(VMIME_64BIT_TYPE "long")
+	ELSE()
+		IF(SIZEOF_LONG_LONG EQUAL 8)
+			SET(VMIME_64BIT_TYPE "long long")
+		ELSE()
+			IF(SIZEOF___INT64 EQUAL 8)
+				SET(VMIME_64BIT_TYPE "__int64")
+			ELSE()
+				MESSAGE(FATAL_ERROR "Cannot determine 64-bit type")
+			ENDIF()
+		ENDIF()
+	ENDIF()
+ENDIF()
 
 
 INCLUDE(cmake/TargetArch.cmake)
diff --git a/SConstruct b/SConstruct
index 4cb82020..6f8b83ac 100644
--- a/SConstruct
+++ b/SConstruct
@@ -605,6 +605,14 @@ opts.AddVariables(
 		map = { },
 		ignorecase = 1
 	),
+	EnumVariable(
+		'pf_64bit_type',
+		'The C-language 64-bit type for your platform',
+		'long',
+		allowed_values = ('char', 'short', 'int', 'long', 'long long'),
+		map = { },
+		ignorecase = 1
+	),
 	EnumVariable(
 		'build_tests',
 		'Build unit tests (run with "scons run-tests")',
@@ -876,6 +884,9 @@ config_hpp.write('typedef unsigned ' + env['pf_16bit_type'] + ' vmime_uint16;\n'
 config_hpp.write('// -- 32-bit\n')
 config_hpp.write('typedef signed ' + env['pf_32bit_type'] + ' vmime_int32;\n')
 config_hpp.write('typedef unsigned ' + env['pf_32bit_type'] + ' vmime_uint32;\n')
+config_hpp.write('// -- 64-bit\n')
+config_hpp.write('typedef signed ' + env['pf_64bit_type'] + ' vmime_int64;\n')
+config_hpp.write('typedef unsigned ' + env['pf_64bit_type'] + ' vmime_uint64;\n')
 config_hpp.write('\n')
 config_hpp.write('#define VMIME_HAVE_SIZE_T 1\n')
 config_hpp.write('\n')
diff --git a/cmake/config.hpp.cmake b/cmake/config.hpp.cmake
index cddf7ef1..d1b235cf 100644
--- a/cmake/config.hpp.cmake
+++ b/cmake/config.hpp.cmake
@@ -37,6 +37,9 @@ typedef unsigned @VMIME_16BIT_TYPE@ vmime_uint16;
 // -- 32-bit
 typedef signed @VMIME_32BIT_TYPE@ vmime_int32;
 typedef unsigned @VMIME_32BIT_TYPE@ vmime_uint32;
+// -- 64-bit
+typedef signed @VMIME_64BIT_TYPE@ vmime_int64;
+typedef unsigned @VMIME_64BIT_TYPE@ vmime_uint64;
 
 #cmakedefine01 VMIME_HAVE_SIZE_T