5 files changed, 17 insertions, 5 deletions
diff --git a/src/build-data/os/mingw.txt b/src/build-data/os/mingw.txt
index 1268298cb..59d9db348 100644
--- a/src/build-data/os/mingw.txt
+++ b/src/build-data/os/mingw.txt
@@ -20,6 +20,7 @@ mingw32
 </aliases>
 
 <target_features>
+cryptgenrandom
 loadlibrary
 win32_virtual_lock
 win32_get_systemtime
diff --git a/src/build-data/os/windows.txt b/src/build-data/os/windows.txt
index bba2e14ec..5afd2596b 100644
--- a/src/build-data/os/windows.txt
+++ b/src/build-data/os/windows.txt
@@ -11,6 +11,7 @@ install_cmd_data "copy"
 install_cmd_exec "copy"
 
 <target_features>
+cryptgenrandom
 gmtime_s
 loadlibrary
 query_perf_counter
diff --git a/src/lib/rng/system_rng/info.txt b/src/lib/rng/system_rng/info.txt
index 387b7e1dd..a452a7d9b 100644
--- a/src/lib/rng/system_rng/info.txt
+++ b/src/lib/rng/system_rng/info.txt
@@ -1,5 +1,7 @@
 define SYSTEM_RNG 20141202
 
+# Any system with /dev/random or CryptGenRandom
+
 <os>
 aix
 cygwin
@@ -11,9 +13,11 @@ hpux
 hurd
 irix
 linux
+mingw
 netbsd
 openbsd
 qnx
 solaris
 tru64
+windows
 </os>
diff --git a/src/lib/rng/system_rng/system_rng.cpp b/src/lib/rng/system_rng/system_rng.cpp
index cdf85ef29..70222530c 100644
--- a/src/lib/rng/system_rng/system_rng.cpp
+++ b/src/lib/rng/system_rng/system_rng.cpp
@@ -7,7 +7,7 @@
 
 #include <botan/system_rng.h>
 
-#if defined(BOTAN_TARGET_OS_IS_WINDOWS)
+#if defined(BOTAN_TARGET_OS_HAS_CRYPTGENRANDOM)
 
 #include <windows.h>
 #include <wincrypt.h>
@@ -45,7 +45,7 @@ class System_RNG : public RandomNumberGenerator
       void add_entropy(const byte[], size_t) {}
    private:
 
-#if defined(BOTAN_TARGET_OS_IS_WINDOWS)
+#if defined(BOTAN_TARGET_OS_HAS_CRYPTGENRANDOM)
       HCRYPTPROV m_prov;
 #else
       int m_fd;
@@ -54,7 +54,7 @@ class System_RNG : public RandomNumberGenerator
 
 System_RNG::System_RNG()
    {
-#if defined(BOTAN_TARGET_OS_IS_WINDOWS)
+#if defined(BOTAN_TARGET_OS_HAS_CRYPTGENRANDOM)
 
    if(!CryptAcquireContext(&m_prov, 0, 0, RSA_FULL, CRYPT_VERIFYCONTEXT))
       throw std::runtime_error("System_RNG failed to acquire crypto provider");
@@ -69,16 +69,17 @@ System_RNG::System_RNG()
 
 System_RNG::~System_RNG()
    {
-#if defined(BOTAN_TARGET_OS_IS_WINDOWS)
+#if defined(BOTAN_TARGET_OS_HAS_CRYPTGENRANDOM)
    ::CryptReleaseContext(m_prov, 0);
 #else
    ::close(m_fd);
+   m_fd = -1;
 #endif
    }
 
 void System_RNG::randomize(byte buf[], size_t len)
    {
-#if defined(BOTAN_TARGET_OS_IS_WINDOWS)
+#if defined(BOTAN_TARGET_OS_HAS_CRYPTGENRANDOM)
    ::CryptGenRandom(m_prov, static_cast<DWORD>(len), buf))
 #else
    while(len)
diff --git a/src/lib/rng/system_rng/system_rng.h b/src/lib/rng/system_rng/system_rng.h
index 6b4746a9c..db91b4ad3 100644
--- a/src/lib/rng/system_rng/system_rng.h
+++ b/src/lib/rng/system_rng/system_rng.h
@@ -12,6 +12,11 @@
 
 namespace Botan {
 
+/**
+* Return a shared reference to a global PRNG instance provided by the
+* operating system. For instance might be instantiated by /dev/urandom
+* or CryptGenRandom.
+*/
 BOTAN_DLL RandomNumberGenerator& system_rng();
 
 }